python/libghdl/thin/vhdl/pyutils.py


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from ctypes import (c_char_p, c_int32, c_int, c_bool, sizeof, c_void_p, byref)
import libghdl.thin.name_table as name_table
import libghdl.thin.vhdl.nodes as nodes
import libghdl.thin.vhdl.nodes_meta as nodes_meta
import libghdl.thin.vhdl.lists as lists
import libghdl.thin.vhdl.flists as flists
from libghdl.thin.vhdl.nodes_meta import (Attr, types)

def name_image(nameid):
    return name_table.Get_Name_Ptr(nameid).decode('utf-8')

def _build_enum_image(cls):
    d = [e for e in dir(cls) if e[0] != '_']
    res = [None] * len(d)
    for e in d:
        res[getattr(cls, e)] = e
    return res


_fields_image = _build_enum_image(nodes_meta.fields)


def fields_image(idx):
    """String representation of field idx"""
    return _fields_image[idx]


_kind_image = _build_enum_image(nodes.Iir_Kind)


def kind_image(k):
    """String representation of Iir_Kind k"""
    return _kind_image[k]


_types_image = _build_enum_image(nodes_meta.types)


def types_image(t):
    """String representation of Nodes_Meta.Types t"""
    return _types_image[t]


_attr_image = _build_enum_image(nodes_meta.Attr)


def attr_image(a):
    """String representation of Nodes_Meta.Attr a"""
    return _attr_image[a]


def leftest_location(n):
    while True:
        if n == Null_Iir:
            return No_Location
        k = nodes.Get_Kind(n)
        if k == nodes.Iir_Kind.Array_Subtype_Definition:
            n = nodes.Get_Subtype_Type_Mark(n)
        else:
            return nodes.Get_Location(n)


def fields_iter(n):
    """Iterate on fields of node n"""
    if n == nodes.Null_Iir:
        return
    k = nodes.Get_Kind(n)
    first = nodes_meta.get_fields_first(k)
    last = nodes_meta.get_fields_last(k)
    for i in range(first, last + 1):
        yield nodes_meta.get_field_by_index(i)


def chain_iter(n):
    """Iterate of a chain headed by node n"""
    while n != nodes.Null_Iir:
        yield n
        n = nodes.Get_Chain(n)


def chain_to_list(n):
    """Convert a chain headed by node n to a python list"""
    return [e for e in chain_iter(n)]


def nodes_iter(n):
    """Iterate of all nodes of n, including n.
    Nodes are returned only once."""
    if n == nodes.Null_Iir:
        return
#    print 'nodes_iter for {0}'.format(n)
    yield n
    for f in fields_iter(n):
        typ = nodes_meta.get_field_type(f)
#        print ' {0}: field {1} (type: {2})'.format(
#            n, fields_image(f), types_image(typ))
        if typ == nodes_meta.types.Iir:
            attr = nodes_meta.get_field_attribute(f)
            if attr == Attr.ANone:
                for n1 in nodes_iter(nodes_meta.Get_Iir(n, f)):
                    yield n1
            elif attr == Attr.Chain:
                n2 = nodes_meta.Get_Iir(n, f)
                while n2 != nodes.Null_Iir:
                    for n1 in nodes_iter(n2):
                        yield n1
                    n2 = nodes.Get_Chain(n2)
            elif attr == Attr.Maybe_Ref:
                if not nodes.Get_Is_Ref(n, f):
                    for n1 in nodes_iter(nodes_meta.Get_Iir(n, f)):
                        yield n1
        elif typ == types.Iir_List:
            attr = nodes_meta.get_field_attribute(f)
            if attr == Attr.ANone:
                for n1 in list_iter(nodes_meta.Get_Iir_List(n, f)):
                    for n2 in nodes_iter(n1):
                        yield n2
        elif typ == types.Iir_Flist:
            attr = nodes_meta.get_field_attribute(f)
            if attr == Attr.ANone:
                for n1 in flist_iter(nodes_meta.Get_Iir_Flist(n, f)):
                    for n2 in nodes_iter(n1):
                        yield n2


def list_iter(lst):
    """Iterate of all element of Iir_List lst."""
    if lst <= nodes.Iir_List_All:
        return
    iter = lists.Iterate(lst)
    while lists.Is_Valid(byref(iter)):
        yield lists.Get_Element(byref(iter))
        lists.Next(byref(iter))


def flist_iter(lst):
    """Iterate of all element of Iir_List lst."""
    if lst <= nodes.Iir_Flist_All:
        return
    for i in range(flists.Flast(lst) + 1):
        yield flists.Get_Nth_Element(lst, i)


def declarations_iter(n):
    """Iterator on all declarations in n."""
    k = nodes.Get_Kind(n)
    if nodes_meta.Has_Generic_Chain(k):
        for n1 in chain_iter(nodes.Get_Generic_Chain(n)):
            yield n1
    if nodes_meta.Has_Port_Chain(k):
        for n1 in chain_iter(nodes.Get_Port_Chain(n)):
            yield n1
    if nodes_meta.Has_Interface_Declaration_Chain(k):
        for n1 in chain_iter(nodes.Get_Interface_Declaration_Chain(n)):
            yield n1
    if nodes_meta.Has_Declaration_Chain(k):
        for n1 in chain_iter(nodes.Get_Declaration_Chain(n)):
            k1 = nodes.Get_Kind(n1)
            if k1 in nodes.Iir_Kinds.Specification \
               or k1 == nodes.Iir_Kind.Use_Clause:
                # Not a declaration
                pass
            elif k1 == nodes.Iir_Kind.Signal_Attribute_Declaration:
                # Not a declaration
                pass
            elif k1 in [nodes.Iir_Kind.Type_Declaration,
                        nodes.Iir_Kind.Anonymous_Type_Declaration]:
                yield n1
                # Handle nested declarations: record elements, physical units,
                # enumeration literals...
                typ = nodes.Get_Type_Definition(n1)
                for n2 in declarations_iter(n1):
                    yield n2
            else:
                yield n1
                # There can be nested declarations (subprograms)
                for n2 in declarations_iter(n1):
                    yield n2
    if nodes_meta.Has_Concurrent_Statement_Chain(k):
        for n1 in chain_iter(nodes.Get_Concurrent_Statement_Chain(n)):
            for n2 in declarations_iter(n1):
                yield n2
    if nodes_meta.Has_Sequential_Statement_Chain(k):
        for n1 in chain_iter(nodes.Get_Sequential_Statement_Chain(n)):
            for n2 in declarations_iter(n1):
                yield n2
    if nodes_meta.Has_Parameter_Specification(k):
        yield nodes.Get_Parameter_Specification(n)
    if nodes_meta.Has_Generate_Statement_Body(k):
        for n1 in declarations_iter(nodes.Get_Generate_Statement_Body(n)):
            yield n1
    if nodes_meta.Has_Else_Clause(k):
        n1 = nodes.Get_Else_Clause(n)
        if n1 != Null_Iir:
            for n2 in declarations_iter(n1):
                yield n2
    if nodes_meta.Has_Generate_Else_Clause(k):
        n1 = nodes.Get_Generate_Else_Clause(n)
        if n1 != Null_Iir:
            for n2 in declarations_iter(n1):
                yield n2
    if nodes_meta.Has_Block_Header(k):
        n1 = nodes.Get_Block_Header(n)
        if n1 != Null_Iir:
            for n2 in declarations_iter(n1):
                yield n2
    # All these nodes are handled:
    if k in [nodes.Iir_Kind.Entity_Declaration,
             nodes.Iir_Kind.Architecture_Body,
             nodes.Iir_Kind.Package_Declaration,
             nodes.Iir_Kind.Package_Body,
             nodes.Iir_Kind.Process_Statement,
             nodes.Iir_Kind.Sensitized_Process_Statement,
             nodes.Iir_Kind.Concurrent_Assertion_Statement,
             nodes.Iir_Kind.Concurrent_Simple_Signal_Assignment,
             nodes.Iir_Kind.Concurrent_Selected_Signal_Assignment,
             nodes.Iir_Kind.Concurrent_Conditional_Signal_Assignment,
             nodes.Iir_Kind.Concurrent_Procedure_Call_Statement,
             nodes.Iir_Kind.Block_Statement,
             nodes.Iir_Kind.Block_Header,
             nodes.Iir_Kind.For_Generate_Statement,
             nodes.Iir_Kind.If_Generate_Statement,
             nodes.Iir_Kind.Generate_Statement_Body,
             nodes.Iir_Kind.Assertion_Statement,
             nodes.Iir_Kind.Wait_Statement,
             nodes.Iir_Kind.Simple_Signal_Assignment_Statement,
             nodes.Iir_Kind.Variable_Assignment_Statement,
             nodes.Iir_Kind.For_Loop_Statement,
             nodes.Iir_Kind.While_Loop_Statement,
             nodes.Iir_Kind.Case_Statement,
             nodes.Iir_Kind.Null_Statement,
             nodes.Iir_Kind.Exit_Statement,
             nodes.Iir_Kind.Next_Statement,
             nodes.Iir_Kind.Procedure_Call_Statement,
             nodes.Iir_Kind.Signal_Declaration,
             nodes.Iir_Kind.Constant_Declaration,
             nodes.Iir_Kind.Variable_Declaration,
             nodes.Iir_Kind.File_Declaration,
             nodes.Iir_Kind.Object_Alias_Declaration,
             nodes.Iir_Kind.Attribute_Declaration,
             nodes.Iir_Kind.Component_Declaration,
             nodes.Iir_Kind.Use_Clause,
             nodes.Iir_Kind.If_Statement,
             nodes.Iir_Kind.Elsif,
             nodes.Iir_Kind.Return_Statement,
             nodes.Iir_Kind.Type_Declaration,
             nodes.Iir_Kind.Anonymous_Type_Declaration,
             nodes.Iir_Kind.Subtype_Declaration,
             nodes.Iir_Kind.Function_Declaration,
             nodes.Iir_Kind.Function_Body,
             nodes.Iir_Kind.Procedure_Declaration,
             nodes.Iir_Kind.Procedure_Body,
             nodes.Iir_Kind.Component_Instantiation_Statement,
             ]:
        return
    assert False, "unknown node of kind {}".format(kind_image(k))


def concurrent_stmts_iter(n):
    """Iterator on concurrent statements in n."""
    k = nodes.Get_Kind(n)
    if k == nodes.Iir_Kind.Design_File:
        for n1 in chain_iter(nodes.Get_First_Design_Unit(n)):
            for n2 in concurrent_stmts_iter(n1):
                yield n2
    elif k == nodes.Iir_Kind.Design_Unit:
        for n1 in concurrent_stmts_iter(nodes.Get_Library_Unit(n)):
            yield n1
    elif k == nodes.Iir_Kind.Entity_Declaration \
         or k == nodes.Iir_Kind.Architecture_Body \
         or k == nodes.Iir_Kind.Block_Statement:
        for n1 in chain_iter(nodes.Get_Concurrent_Statement_Chain(n)):
            yield n1
            for n2 in concurrent_stmts_iter(n1):
                yield n2
    elif k == nodes.Iir_Kind.For_Generate_Statement:
        for n1 in concurrent_stmts_iter(nodes.Get_Generate_Statement_Body(n)):
            yield n1
    elif k == nodes.Iir_Kind.If_Generate_Statement:
        while n != Null_Iir:
            for n1 in concurrent_stmts_iter(
                    nodes.Get_Generate_Statement_Body(n)):
                yield n1
            n = nodes.Get_Generate_Else_Clause(n)
    elif k == nodes.Iir_Kind.Case_Generate_Statement:
        alt = nodes.Get_Case_Statement_Alternative_Chain(n)
        for n1 in chain_iter(alt):
            blk = nodes.Get_Associated_Block(n1)
            if blk != Null_Iir:
                for n2 in concurrent_stmts_iter(
                        nodes.Get_Generate_Statement_Body(n)):
                    yield n2


def constructs_iter(n):
    """Iterator on library unit, concurrent statements and declarations
       that appear directly within a declarative part."""
    if n == thin.Null_Iir:
        return
    k = nodes.Get_Kind(n)
    if k == nodes.Iir_Kind.Design_File:
        for n1 in chain_iter(nodes.Get_First_Design_Unit(n)):
            for n2 in constructs_iter(n1):
                yield n2
    elif k == nodes.Iir_Kind.Design_Unit:
        n1 = nodes.Get_Library_Unit(n)
        yield n1
        for n2 in constructs_iter(n1):
            yield n2
    elif k in [nodes.Iir_Kind.Entity_Declaration,
               nodes.Iir_Kind.Architecture_Body,
               nodes.Iir_Kind.Block_Statement,
               nodes.Iir_Kind.Generate_Statement_Body]:
        for n1 in chain_iter(nodes.Get_Declaration_Chain(n)):
            yield n1
            for n2 in constructs_iter(n1):
                yield n2
        for n1 in chain_iter(nodes.Get_Concurrent_Statement_Chain(n)):
            yield n1
            for n2 in constructs_iter(n1):
                yield n2
    elif k in [nodes.Iir_Kind.Configuration_Declaration,
               nodes.Iir_Kind.Package_Declaration,
               nodes.Iir_Kind.Package_Body,
               nodes.Iir_Kind.Function_Body,
               nodes.Iir_Kind.Procedure_Body,
               nodes.Iir_Kind.Protected_Type_Declaration,
               nodes.Iir_Kind.Protected_Type_Body,
               nodes.Iir_Kind.Process_Statement,
               nodes.Iir_Kind.Sensitized_Process_Statement]:
        for n1 in chain_iter(nodes.Get_Declaration_Chain(n)):
            yield n1
            for n2 in constructs_iter(n1):
                yield n2
    elif k == nodes.Iir_Kind.For_Generate_Statement:
        n1 = nodes.Get_Generate_Statement_Body(n)
        yield n1
        for n2 in constructs_iter(n1):
            yield n2
    elif k == nodes.Iir_Kind.If_Generate_Statement:
        while n != Null_Iir:
            n1 = nodes.Get_Generate_Statement_Body(n)
            yield n1
            for n2 in constructs_iter(n1):
                yield n2
            n = nodes.Get_Generate_Else_Clause(n)
    elif k == nodes.Iir_Kind.Case_Generate_Statement:
        alt = nodes.Get_Case_Statement_Alternative_Chain(n)
        for n1 in chain_iter(alt):
            blk = nodes.Get_Associated_Block(n1)
            if blk != Null_Iir:
                n2 = nodes.Get_Generate_Statement_Body(blk)
                yield n2
                for n3 in constructs_iter(n2):
                    yield n3

def sequential_iter(n):
    """Iterator on sequential statements.  The first node must be either
       a process or a subprogram body."""
    if n == thin.Null_Iir:
        return
    k = nodes.Get_Kind(n)
    if k in [nodes.Iir_Kind.Process_Statement,
             nodes.Iir_Kind.Sensitized_Process_Statement,
             nodes.Iir_Kind.Function_Body,
             nodes.Iir_Kind.Procedure_Body]:
        for n1 in chain_iter(nodes.Get_Sequential_Statement_Chain(n)):
            yield n1
            for n2 in sequential_iter(n1):
                yield n2
    elif k == nodes.Iir_Kind.If_Statement:
        while True:
            n = nodes.Get_Chain(n)
            if n == thin.Null_Iir:
                break
            yield n
            for n1 in sequential_iter(n):
                yield n1
    elif k == nodes.Iir_Kind.Case_Statement:
        for ch in chain_iter(nodes.Get_Case_Statement_Alternative_Chain(n)):
            stmt = nodes.Get_Associated_Chain(ch)
            if stmt != thin.Null_Iir:
                for n1 in chain_iter(stmt):
                    yield n1
                    for n2 in sequential_iter(n1):
                        yield n2
    elif k in [nodes.Iir_Kind.For_Loop_Statement,
               nodes.Iir_Kind.While_Loop_Statement]:
        for n1 in chain_iter(nodes.Get_Sequential_Statement_Chain(n)):
            yield n1
            for n2 in sequential_iter(n1):
                yield n2
    elif k in [nodes.Iir_Kind.Assertion_Statement,
               nodes.Iir_Kind.Wait_Statement,
               nodes.Iir_Kind.Null_Statement,
               nodes.Iir_Kind.Exit_Statement,
               nodes.Iir_Kind.Next_Statement,
               nodes.Iir_Kind.Return_Statement,
               nodes.Iir_Kind.Variable_Assignment_Statement,
               nodes.Iir_Kind.Simple_Signal_Assignment_Statement,
               nodes.Iir_Kind.Procedure_Call_Statement]:
        return
    else:
        assert False, "unknown node of kind {}".format(kind_image(k))
# Advanced googletest Topics

<!-- GOOGLETEST_CM0016 DO NOT DELETE -->

## Introduction

Now that you have read the [googletest Primer](primer.md) and learned how to
write tests using googletest, it's time to learn some new tricks. This document
will show you more assertions as well as how to construct complex failure
messages, propagate fatal failures, reuse and speed up your test fixtures, and
use various flags with your tests.

## More Assertions

This section covers some less frequently used, but still significant,
assertions.

### Explicit Success and Failure

These three assertions do not actually test a value or expression. Instead, they
generate a success or failure directly. Like the macros that actually perform a
test, you may stream a custom failure message into them.

```c++
SUCCEED();
```

Generates a success. This does **NOT** make the overall test succeed. A test is
considered successful only if none of its assertions fail during its execution.

NOTE: `SUCCEED()` is purely documentary and currently doesn't generate any
user-visible output. However, we may add `SUCCEED()` messages to googletest's
output in the future.

```c++
FAIL();
ADD_FAILURE();
ADD_FAILURE_AT("file_path", line_number);
```

`FAIL()` generates a fatal failure, while `ADD_FAILURE()` and `ADD_FAILURE_AT()`
generate a nonfatal failure. These are useful when control flow, rather than a
Boolean expression, determines the test's success or failure. For example, you
might want to write something like:

```c++
switch(expression) {
  case 1:
     ... some checks ...
  case 2:
     ... some other checks ...
  default:
     FAIL() << "We shouldn't get here.";
}
```

NOTE: you can only use `FAIL()` in functions that return `void`. See the
[Assertion Placement section](#assertion-placement) for more information.

### Exception Assertions

These are for verifying that a piece of code throws (or does not throw) an
exception of the given type:

Fatal assertion                            | Nonfatal assertion                         | Verifies
------------------------------------------ | ------------------------------------------ | --------
`ASSERT_THROW(statement, exception_type);` | `EXPECT_THROW(statement, exception_type);` | `statement` throws an exception of the given type
`ASSERT_ANY_THROW(statement);`             | `EXPECT_ANY_THROW(statement);`             | `statement` throws an exception of any type
`ASSERT_NO_THROW(statement);`              | `EXPECT_NO_THROW(statement);`              | `statement` doesn't throw any exception

Examples:

```c++
ASSERT_THROW(Foo(5), bar_exception);

EXPECT_NO_THROW({
  int n = 5;
  Bar(&n);
});
```

**Availability**: requires exceptions to be enabled in the build environment

### Predicate Assertions for Better Error Messages

Even though googletest has a rich set of assertions, they can never be complete,
as it's impossible (nor a good idea) to anticipate all scenarios a user might
run into. Therefore, sometimes a user has to use `EXPECT_TRUE()` to check a
complex expression, for lack of a better macro. This has the problem of not
showing you the values of the parts of the expression, making it hard to
understand what went wrong. As a workaround, some users choose to construct the
failure message by themselves, streaming it into `EXPECT_TRUE()`. However, this
is awkward especially when the expression has side-effects or is expensive to
evaluate.

googletest gives you three different options to solve this problem:

#### Using an Existing Boolean Function

If you already have a function or functor that returns `bool` (or a type that
can be implicitly converted to `bool`), you can use it in a *predicate
assertion* to get the function arguments printed for free:

<!-- mdformat off(github rendering does not support multiline tables) -->

| Fatal assertion                   | Nonfatal assertion                | Verifies                    |
| --------------------------------- | --------------------------------- | --------------------------- |
| `ASSERT_PRED1(pred1, val1)`       | `EXPECT_PRED1(pred1, val1)`       | `pred1(val1)` is true       |
| `ASSERT_PRED2(pred2, val1, val2)` | `EXPECT_PRED2(pred2, val1, val2)` | `pred2(val1, val2)` is true |
| `...`                             | `...`                             | `...`                       |

<!-- mdformat on-->
In the above, `predn` is an `n`-ary predicate function or functor, where `val1`,
`val2`, ..., and `valn` are its arguments. The assertion succeeds if the
predicate returns `true` when applied to the given arguments, and fails
otherwise. When the assertion fails, it prints the value of each argument. In
either case, the arguments are evaluated exactly once.

Here's an example. Given

```c++
// Returns true if m and n have no common divisors except 1.
bool MutuallyPrime(int m, int n) { ... }

const int a = 3;
const int b = 4;
const int c = 10;
```

the assertion

```c++
  EXPECT_PRED2(MutuallyPrime, a, b);
```

will succeed, while the assertion

```c++
  EXPECT_PRED2(MutuallyPrime, b, c);
```

will fail with the message

```none
MutuallyPrime(b, c) is false, where
b is 4
c is 10
```

> NOTE:
>
> 1.  If you see a compiler error "no matching function to call" when using
>     `ASSERT_PRED*` or `EXPECT_PRED*`, please see
>     [this](faq.md#the-compiler-complains-no-matching-function-to-call-when-i-use-assert-pred-how-do-i-fix-it)
>     for how to resolve it.

#### Using a Function That Returns an AssertionResult

While `EXPECT_PRED*()` and friends are handy for a quick job, the syntax is not
satisfactory: you have to use different macros for different arities, and it
feels more like Lisp than C++. The `::testing::AssertionResult` class solves
this problem.

An `AssertionResult` object represents the result of an assertion (whether it's
a success or a failure, and an associated message). You can create an
`AssertionResult` using one of these factory functions:

```c++
namespace testing {

// Returns an AssertionResult object to indicate that an assertion has
// succeeded.
AssertionResult AssertionSuccess();

// Returns an AssertionResult object to indicate that an assertion has
// failed.
AssertionResult AssertionFailure();

}
```

You can then use the `<<` operator to stream messages to the `AssertionResult`
object.

To provide more readable messages in Boolean assertions (e.g. `EXPECT_TRUE()`),
write a predicate function that returns `AssertionResult` instead of `bool`. For
example, if you define `IsEven()` as:

```c++
::testing::AssertionResult IsEven(int n) {
  if ((n % 2) == 0)
     return ::testing::AssertionSuccess();
  else
     return ::testing::AssertionFailure() << n << " is odd";
}
```

instead of:

```c++
bool IsEven(int n) {
  return (n % 2) == 0;
}
```

the failed assertion `EXPECT_TRUE(IsEven(Fib(4)))` will print:

```none
Value of: IsEven(Fib(4))
  Actual: false (3 is odd)
Expected: true
```

instead of a more opaque

```none
Value of: IsEven(Fib(4))
  Actual: false
Expected: true
```

If you want informative messages in `EXPECT_FALSE` and `ASSERT_FALSE` as well
(one third of Boolean assertions in the Google code base are negative ones), and
are fine with making the predicate slower in the success case, you can supply a
success message:

```c++
::testing::AssertionResult IsEven(int n) {
  if ((n % 2) == 0)
     return ::testing::AssertionSuccess() << n << " is even";
  else
     return ::testing::AssertionFailure() << n << " is odd";
}
```

Then the statement `EXPECT_FALSE(IsEven(Fib(6)))` will print

```none
  Value of: IsEven(Fib(6))
     Actual: true (8 is even)
  Expected: false
```

#### Using a Predicate-Formatter

If you find the default message generated by `(ASSERT|EXPECT)_PRED*` and
`(ASSERT|EXPECT)_(TRUE|FALSE)` unsatisfactory, or some arguments to your
predicate do not support streaming to `ostream`, you can instead use the
following *predicate-formatter assertions* to *fully* customize how the message
is formatted:

Fatal assertion                                  | Nonfatal assertion                               | Verifies
------------------------------------------------ | ------------------------------------------------ | --------
`ASSERT_PRED_FORMAT1(pred_format1, val1);`       | `EXPECT_PRED_FORMAT1(pred_format1, val1);`       | `pred_format1(val1)` is successful
`ASSERT_PRED_FORMAT2(pred_format2, val1, val2);` | `EXPECT_PRED_FORMAT2(pred_format2, val1, val2);` | `pred_format2(val1, val2)` is successful
`...`                                            | `...`                                            | ...

The difference between this and the previous group of macros is that instead of
a predicate, `(ASSERT|EXPECT)_PRED_FORMAT*` take a *predicate-formatter*
(`pred_formatn`), which is a function or functor with the signature:

```c++
::testing::AssertionResult PredicateFormattern(const char* expr1,
                                               const char* expr2,
                                               ...
                                               const char* exprn,
                                               T1 val1,
                                               T2 val2,
                                               ...
                                               Tn valn);
```

where `val1`, `val2`, ..., and `valn` are the values of the predicate arguments,
and `expr1`, `expr2`, ..., and `exprn` are the corresponding expressions as they
appear in the source code. The types `T1`, `T2`, ..., and `Tn` can be either
value types or reference types. For example, if an argument has type `Foo`, you
can declare it as either `Foo` or `const Foo&`, whichever is appropriate.

As an example, let's improve the failure message in `MutuallyPrime()`, which was
used with `EXPECT_PRED2()`:

```c++
// Returns the smallest prime common divisor of m and n,
// or 1 when m and n are mutually prime.
int SmallestPrimeCommonDivisor(int m, int n) { ... }

// A predicate-formatter for asserting that two integers are mutually prime.
::testing::AssertionResult AssertMutuallyPrime(const char* m_expr,
                                               const char* n_expr,
                                               int m,
                                               int n) {
  if (MutuallyPrime(m, n)) return ::testing::AssertionSuccess();

  return ::testing::AssertionFailure() << m_expr << " and " << n_expr
      << " (" << m << " and " << n << ") are not mutually prime, "
      << "as they have a common divisor " << SmallestPrimeCommonDivisor(m, n);
}
```

With this predicate-formatter, we can use

```c++
  EXPECT_PRED_FORMAT2(AssertMutuallyPrime, b, c);
```

to generate the message

```none
b and c (4 and 10) are not mutually prime, as they have a common divisor 2.
```

As you may have realized, many of the built-in assertions we introduced earlier
are special cases of `(EXPECT|ASSERT)_PRED_FORMAT*`. In fact, most of them are
indeed defined using `(EXPECT|ASSERT)_PRED_FORMAT*`.

### Floating-Point Comparison

Comparing floating-point numbers is tricky. Due to round-off errors, it is very
unlikely that two floating-points will match exactly. Therefore, `ASSERT_EQ` 's
naive comparison usually doesn't work. And since floating-points can have a wide
value range, no single fixed error bound works. It's better to compare by a
fixed relative error bound, except for values close to 0 due to the loss of
precision there.

In general, for floating-point comparison to make sense, the user needs to
carefully choose the error bound. If they don't want or care to, comparing in
terms of Units in the Last Place (ULPs) is a good default, and googletest
provides assertions to do this. Full details about ULPs are quite long; if you
want to learn more, see
[here](https://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/).

#### Floating-Point Macros

<!-- mdformat off(github rendering does not support multiline tables) -->

| Fatal assertion                 | Nonfatal assertion              | Verifies                                 |
| ------------------------------- | ------------------------------- | ---------------------------------------- |
| `ASSERT_FLOAT_EQ(val1, val2);`  | `EXPECT_FLOAT_EQ(val1, val2);`  | the two `float` values are almost equal  |
| `ASSERT_DOUBLE_EQ(val1, val2);` | `EXPECT_DOUBLE_EQ(val1, val2);` | the two `double` values are almost equal |

<!-- mdformat on-->

By "almost equal" we mean the values are within 4 ULP's from each other.

The following assertions allow you to choose the acceptable error bound:

<!-- mdformat off(github rendering does not support multiline tables) -->

| Fatal assertion                       | Nonfatal assertion                    | Verifies                                                                         |
| ------------------------------------- | ------------------------------------- | -------------------------------------------------------------------------------- |
| `ASSERT_NEAR(val1, val2, abs_error);` | `EXPECT_NEAR(val1, val2, abs_error);` | the difference between `val1` and `val2` doesn't exceed the given absolute error |

<!-- mdformat on-->

#### Floating-Point Predicate-Format Functions

Some floating-point operations are useful, but not that often used. In order to
avoid an explosion of new macros, we provide them as predicate-format functions
that can be used in predicate assertion macros (e.g. `EXPECT_PRED_FORMAT2`,
etc).

```c++
EXPECT_PRED_FORMAT2(::testing::FloatLE, val1, val2);
EXPECT_PRED_FORMAT2(::testing::DoubleLE, val1, val2);
```

Verifies that `val1` is less than, or almost equal to, `val2`. You can replace
`EXPECT_PRED_FORMAT2` in the above table with `ASSERT_PRED_FORMAT2`.

### Asserting Using gMock Matchers

[gMock](../../googlemock) comes with a library of matchers for validating
arguments passed to mock objects. A gMock *matcher* is basically a predicate
that knows how to describe itself. It can be used in these assertion macros:

<!-- mdformat off(github rendering does not support multiline tables) -->

| Fatal assertion                | Nonfatal assertion             | Verifies              |
| ------------------------------ | ------------------------------ | --------------------- |
| `ASSERT_THAT(value, matcher);` | `EXPECT_THAT(value, matcher);` | value matches matcher |

<!-- mdformat on-->

For example, `StartsWith(prefix)` is a matcher that matches a string starting
with `prefix`, and you can write:

```c++
using ::testing::StartsWith;
...
    // Verifies that Foo() returns a string starting with "Hello".
    EXPECT_THAT(Foo(), StartsWith("Hello"));
```

Read this
[recipe](../../googlemock/docs/cook_book.md#using-matchers-in-googletest-assertions)
in the gMock Cookbook for more details.

gMock has a rich set of matchers. You can do many things googletest cannot do
alone with them. For a list of matchers gMock provides, read
[this](../../googlemock/docs/cook_book.md##using-matchers). It's easy to write
your [own matchers](../../googlemock/docs/cook_book.md#NewMatchers) too.

gMock is bundled with googletest, so you don't need to add any build dependency
in order to take advantage of this. Just include `"testing/base/public/gmock.h"`
and you're ready to go.

### More String Assertions

(Please read the [previous](#asserting-using-gmock-matchers) section first if
you haven't.)

You can use the gMock
[string matchers](../../googlemock/docs/cheat_sheet.md#string-matchers) with
`EXPECT_THAT()` or `ASSERT_THAT()` to do more string comparison tricks
(sub-string, prefix, suffix, regular expression, and etc). For example,

```c++
using ::testing::HasSubstr;
using ::testing::MatchesRegex;
...
  ASSERT_THAT(foo_string, HasSubstr("needle"));
  EXPECT_THAT(bar_string, MatchesRegex("\\w*\\d+"));
```

If the string contains a well-formed HTML or XML document, you can check whether
its DOM tree matches an
[XPath expression](http://www.w3.org/TR/xpath/#contents):

```c++
// Currently still in //template/prototemplate/testing:xpath_matcher
#include "template/prototemplate/testing/xpath_matcher.h"
using prototemplate::testing::MatchesXPath;
EXPECT_THAT(html_string, MatchesXPath("//a[text()='click here']"));
```

### Windows HRESULT assertions

These assertions test for `HRESULT` success or failure.

Fatal assertion                        | Nonfatal assertion                     | Verifies
-------------------------------------- | -------------------------------------- | --------
`ASSERT_HRESULT_SUCCEEDED(expression)` | `EXPECT_HRESULT_SUCCEEDED(expression)` | `expression` is a success `HRESULT`
`ASSERT_HRESULT_FAILED(expression)`    | `EXPECT_HRESULT_FAILED(expression)`    | `expression` is a failure `HRESULT`

The generated output contains the human-readable error message associated with
the `HRESULT` code returned by `expression`.

You might use them like this:

```c++
CComPtr<IShellDispatch2> shell;
ASSERT_HRESULT_SUCCEEDED(shell.CoCreateInstance(L"Shell.Application"));
CComVariant empty;
ASSERT_HRESULT_SUCCEEDED(shell->ShellExecute(CComBSTR(url), empty, empty, empty, empty));
```

### Type Assertions

You can call the function

```c++
::testing::StaticAssertTypeEq<T1, T2>();
```

to assert that types `T1` and `T2` are the same. The function does nothing if
the assertion is satisfied. If the types are different, the function call will
fail to compile, the compiler error message will say that
`T1 and T2 are not the same type` and most likely (depending on the compiler)
show you the actual values of `T1` and `T2`. This is mainly useful inside
template code.

**Caveat**: When used inside a member function of a class template or a function
template, `StaticAssertTypeEq<T1, T2>()` is effective only if the function is
instantiated. For example, given:

```c++
template <typename T> class Foo {
 public:
  void Bar() { ::testing::StaticAssertTypeEq<int, T>(); }
};
```

the code:

```c++
void Test1() { Foo<bool> foo; }
```

will not generate a compiler error, as `Foo<bool>::Bar()` is never actually
instantiated. Instead, you need:

```c++
void Test2() { Foo<bool> foo; foo.Bar(); }
```

to cause a compiler error.

### Assertion Placement

You can use assertions in any C++ function. In particular, it doesn't have to be
a method of the test fixture class. The one constraint is that assertions that
generate a fatal failure (`FAIL*` and `ASSERT_*`) can only be used in
void-returning functions. This is a consequence of Google's not using
exceptions. By placing it in a non-void function you'll get a confusing compile
error like `"error: void value not ignored as it ought to be"` or `"cannot
initialize return object of type 'bool' with an rvalue of type 'void'"` or
`"error: no viable conversion from 'void' to 'string'"`.

If you need to use fatal assertions in a function that returns non-void, one
option is to make the function return the value in an out parameter instead. For
example, you can rewrite `T2 Foo(T1 x)` to `void Foo(T1 x, T2* result)`. You
need to make sure that `*result` contains some sensible value even when the
function returns prematurely. As the function now returns `void`, you can use
any assertion inside of it.

If changing the function's type is not an option, you should just use assertions
that generate non-fatal failures, such as `ADD_FAILURE*` and `EXPECT_*`.

NOTE: Constructors and destructors are not considered void-returning functions,
according to the C++ language specification, and so you may not use fatal
assertions in them; you'll get a compilation error if you try. Instead, either
call `abort` and crash the entire test executable, or put the fatal assertion in
a `SetUp`/`TearDown` function; see
[constructor/destructor vs. `SetUp`/`TearDown`](faq.md#CtorVsSetUp)

WARNING: A fatal assertion in a helper function (private void-returning method)
called from a constructor or destructor does not does not terminate the current
test, as your intuition might suggest: it merely returns from the constructor or
destructor early, possibly leaving your object in a partially-constructed or
partially-destructed state! You almost certainly want to `abort` or use
`SetUp`/`TearDown` instead.

## Teaching googletest How to Print Your Values

When a test assertion such as `EXPECT_EQ` fails, googletest prints the argument
values to help you debug. It does this using a user-extensible value printer.

This printer knows how to print built-in C++ types, native arrays, STL
containers, and any type that supports the `<<` operator. For other types, it
prints the raw bytes in the value and hopes that you the user can figure it out.

As mentioned earlier, the printer is *extensible*. That means you can teach it
to do a better job at printing your particular type than to dump the bytes. To
do that, define `<<` for your type:

```c++
#include <ostream>

namespace foo {

class Bar {  // We want googletest to be able to print instances of this.
...
  // Create a free inline friend function.
  friend std::ostream& operator<<(std::ostream& os, const Bar& bar) {
    return os << bar.DebugString();  // whatever needed to print bar to os
  }
};

// If you can't declare the function in the class it's important that the
// << operator is defined in the SAME namespace that defines Bar.  C++'s look-up
// rules rely on that.
std::ostream& operator<<(std::ostream& os, const Bar& bar) {
  return os << bar.DebugString();  // whatever needed to print bar to os
}

}  // namespace foo
```

Sometimes, this might not be an option: your team may consider it bad style to
have a `<<` operator for `Bar`, or `Bar` may already have a `<<` operator that
doesn't do what you want (and you cannot change it). If so, you can instead
define a `PrintTo()` function like this:

```c++
#include <ostream>

namespace foo {

class Bar {
  ...
  friend void PrintTo(const Bar& bar, std::ostream* os) {
    *os << bar.DebugString();  // whatever needed to print bar to os
  }
};

// If you can't declare the function in the class it's important that PrintTo()
// is defined in the SAME namespace that defines Bar.  C++'s look-up rules rely
// on that.
void PrintTo(const Bar& bar, std::ostream* os) {
  *os << bar.DebugString();  // whatever needed to print bar to os
}

}  // namespace foo
```

If you have defined both `<<` and `PrintTo()`, the latter will be used when
googletest is concerned. This allows you to customize how the value appears in
googletest's output without affecting code that relies on the behavior of its
`<<` operator.

If you want to print a value `x` using googletest's value printer yourself, just
call `::testing::PrintToString(x)`, which returns an `std::string`:

```c++
vector<pair<Bar, int> > bar_ints = GetBarIntVector();

EXPECT_TRUE(IsCorrectBarIntVector(bar_ints))
    << "bar_ints = " << ::testing::PrintToString(bar_ints);
```

## Death Tests

In many applications, there are assertions that can cause application failure if
a condition is not met. These sanity checks, which ensure that the program is in
a known good state, are there to fail at the earliest possible time after some
program state is corrupted. If the assertion checks the wrong condition, then
the program may proceed in an erroneous state, which could lead to memory
corruption, security holes, or worse. Hence it is vitally important to test that
such assertion statements work as expected.

Since these precondition checks cause the processes to die, we call such tests
_death tests_. More generally, any test that checks that a program terminates
(except by throwing an exception) in an expected fashion is also a death test.

Note that if a piece of code throws an exception, we don't consider it "death"
for the purpose of death tests, as the caller of the code could catch the
exception and avoid the crash. If you want to verify exceptions thrown by your
code, see [Exception Assertions](#ExceptionAssertions).

If you want to test `EXPECT_*()/ASSERT_*()` failures in your test code, see
Catching Failures

### How to Write a Death Test

googletest has the following macros to support death tests:

Fatal assertion                                  | Nonfatal assertion                               | Verifies
------------------------------------------------ | ------------------------------------------------ | --------
`ASSERT_DEATH(statement, matcher);`              | `EXPECT_DEATH(statement, matcher);`              | `statement` crashes with the given error
`ASSERT_DEATH_IF_SUPPORTED(statement, matcher);` | `EXPECT_DEATH_IF_SUPPORTED(statement, matcher);` | if death tests are supported, verifies that `statement` crashes with the given error; otherwise verifies nothing
`ASSERT_DEBUG_DEATH(statement, matcher);`        | `EXPECT_DEBUG_DEATH(statement, matcher);`        | `statement` crashes with the given error **in debug mode**. When not in debug (i.e. `NDEBUG` is defined), this just executes `statement`
`ASSERT_EXIT(statement, predicate, matcher);`    | `EXPECT_EXIT(statement, predicate, matcher);`    | `statement` exits with the given error, and its exit code matches `predicate`

where `statement` is a statement that is expected to cause the process to die,
`predicate` is a function or function object that evaluates an integer exit
status, and `matcher` is either a gMock matcher matching a `const std::string&`
or a (Perl) regular expression - either of which is matched against the stderr
output of `statement`. For legacy reasons, a bare string (i.e. with no matcher)
is interpreted as `ContainsRegex(str)`, **not** `Eq(str)`. Note that `statement`
can be *any valid statement* (including *compound statement*) and doesn't have
to be an expression.

As usual, the `ASSERT` variants abort the current test function, while the
`EXPECT` variants do not.

> NOTE: We use the word "crash" here to mean that the process terminates with a
> *non-zero* exit status code. There are two possibilities: either the process
> has called `exit()` or `_exit()` with a non-zero value, or it may be killed by
> a signal.
>
> This means that if *`statement`* terminates the process with a 0 exit code, it
> is *not* considered a crash by `EXPECT_DEATH`. Use `EXPECT_EXIT` instead if
> this is the case, or if you want to restrict the exit code more precisely.

A predicate here must accept an `int` and return a `bool`. The death test
succeeds only if the predicate returns `true`. googletest defines a few
predicates that handle the most common cases:

```c++
::testing::ExitedWithCode(exit_code)
```

This expression is `true` if the program exited normally with the given exit
code.

```c++
::testing::KilledBySignal(signal_number)  // Not available on Windows.
```

This expression is `true` if the program was killed by the given signal.

The `*_DEATH` macros are convenient wrappers for `*_EXIT` that use a predicate
that verifies the process' exit code is non-zero.

Note that a death test only cares about three things:

1.  does `statement` abort or exit the process?
2.  (in the case of `ASSERT_EXIT` and `EXPECT_EXIT`) does the exit status
    satisfy `predicate`? Or (in the case of `ASSERT_DEATH` and `EXPECT_DEATH`)
    is the exit status non-zero? And
3.  does the stderr output match `matcher`?

In particular, if `statement` generates an `ASSERT_*` or `EXPECT_*` failure, it
will **not** cause the death test to fail, as googletest assertions don't abort
the process.

To write a death test, simply use one of the above macros inside your test
function. For example,

```c++
TEST(MyDeathTest, Foo) {
  // This death test uses a compound statement.
  ASSERT_DEATH({
    int n = 5;
    Foo(&n);
  }, "Error on line .* of Foo()");
}

TEST(MyDeathTest, NormalExit) {
  EXPECT_EXIT(NormalExit(), ::testing::ExitedWithCode(0), "Success");
}

TEST(MyDeathTest, KillMyself) {
  EXPECT_EXIT(KillMyself(), ::testing::KilledBySignal(SIGKILL),
              "Sending myself unblockable signal");
}
```

verifies that:

*   calling `Foo(5)` causes the process to die with the given error message,
*   calling `NormalExit()` causes the process to print `"Success"` to stderr and
    exit with exit code 0, and
*   calling `KillMyself()` kills the process with signal `SIGKILL`.

The test function body may contain other assertions and statements as well, if
necessary.

### Death Test Naming

IMPORTANT: We strongly recommend you to follow the convention of naming your
**test suite** (not test) `*DeathTest` when it contains a death test, as
demonstrated in the above example. The
[Death Tests And Threads](#death-tests-and-threads) section below explains why.

If a test fixture class is shared by normal tests and death tests, you can use
`using` or `typedef` to introduce an alias for the fixture class and avoid
duplicating its code:

```c++
class FooTest : public ::testing::Test { ... };

using FooDeathTest = FooTest;

TEST_F(FooTest, DoesThis) {
  // normal test
}

TEST_F(FooDeathTest, DoesThat) {
  // death test
}
```

### Regular Expression Syntax

On POSIX systems (e.g. Linux, Cygwin, and Mac), googletest uses the
[POSIX extended regular expression](http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap09.html#tag_09_04)
syntax. To learn about this syntax, you may want to read this
[Wikipedia entry](http://en.wikipedia.org/wiki/Regular_expression#POSIX_Extended_Regular_Expressions).

On Windows, googletest uses its own simple regular expression implementation. It
lacks many features. For example, we don't support union (`"x|y"`), grouping
(`"(xy)"`), brackets (`"[xy]"`), and repetition count (`"x{5,7}"`), among
others. Below is what we do support (`A` denotes a literal character, period
(`.`), or a single `\\ ` escape sequence; `x` and `y` denote regular
expressions.):

Expression | Meaning
---------- | --------------------------------------------------------------
`c`        | matches any literal character `c`
`\\d`      | matches any decimal digit
`\\D`      | matches any character that's not a decimal digit
`\\f`      | matches `\f`
`\\n`      | matches `\n`
`\\r`      | matches `\r`
`\\s`      | matches any ASCII whitespace, including `\n`
`\\S`      | matches any character that's not a whitespace
`\\t`      | matches `\t`
`\\v`      | matches `\v`
`\\w`      | matches any letter, `_`, or decimal digit
`\\W`      | matches any character that `\\w` doesn't match
`\\c`      | matches any literal character `c`, which must be a punctuation
`.`        | matches any single character except `\n`
`A?`       | matches 0 or 1 occurrences of `A`
`A*`       | matches 0 or many occurrences of `A`
`A+`       | matches 1 or many occurrences of `A`
`^`        | matches the beginning of a string (not that of each line)
`$`        | matches the end of a string (not that of each line)
`xy`       | matches `x` followed by `y`

To help you determine which capability is available on your system, googletest
defines macros to govern which regular expression it is using. The macros are:
`GTEST_USES_SIMPLE_RE=1` or `GTEST_USES_POSIX_RE=1`. If you want your death
tests to work in all cases, you can either `#if` on these macros or use the more
limited syntax only.

### How It Works

Under the hood, `ASSERT_EXIT()` spawns a new process and executes the death test
statement in that process. The details of how precisely that happens depend on
the platform and the variable ::testing::GTEST_FLAG(death_test_style) (which is
initialized from the command-line flag `--gtest_death_test_style`).

*   On POSIX systems, `fork()` (or `clone()` on Linux) is used to spawn the
    child, after which:
    *   If the variable's value is `"fast"`, the death test statement is
        immediately executed.
    *   If the variable's value is `"threadsafe"`, the child process re-executes
        the unit test binary just as it was originally invoked, but with some
        extra flags to cause just the single death test under consideration to
        be run.
*   On Windows, the child is spawned using the `CreateProcess()` API, and
    re-executes the binary to cause just the single death test under
    consideration to be run - much like the `threadsafe` mode on POSIX.

Other values for the variable are illegal and will cause the death test to fail.
Currently, the flag's default value is **"fast"**

1.  the child's exit status satisfies the predicate, and
2.  the child's stderr matches the regular expression.

If the death test statement runs to completion without dying, the child process
will nonetheless terminate, and the assertion fails.

### Death Tests And Threads

The reason for the two death test styles has to do with thread safety. Due to
well-known problems with forking in the presence of threads, death tests should
be run in a single-threaded context. Sometimes, however, it isn't feasible to
arrange that kind of environment. For example, statically-initialized modules
may start threads before main is ever reached. Once threads have been created,
it may be difficult or impossible to clean them up.

googletest has three features intended to raise awareness of threading issues.

1.  A warning is emitted if multiple threads are running when a death test is
    encountered.
2.  Test suites with a name ending in "DeathTest" are run before all other
    tests.
3.  It uses `clone()` instead of `fork()` to spawn the child process on Linux
    (`clone()` is not available on Cygwin and Mac), as `fork()` is more likely
    to cause the child to hang when the parent process has multiple threads.

It's perfectly fine to create threads inside a death test statement; they are
executed in a separate process and cannot affect the parent.

### Death Test Styles

The "threadsafe" death test style was introduced in order to help mitigate the
risks of testing in a possibly multithreaded environment. It trades increased
test execution time (potentially dramatically so) for improved thread safety.

The automated testing framework does not set the style flag. You can choose a
particular style of death tests by setting the flag programmatically:

```c++
testing::FLAGS_gtest_death_test_style="threadsafe"
```

You can do this in `main()` to set the style for all death tests in the binary,
or in individual tests. Recall that flags are saved before running each test and
restored afterwards, so you need not do that yourself. For example:

```c++
int main(int argc, char** argv) {
  InitGoogle(argv[0], &argc, &argv, true);
  ::testing::FLAGS_gtest_death_test_style = "fast";
  return RUN_ALL_TESTS();
}

TEST(MyDeathTest, TestOne) {
  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
  // This test is run in the "threadsafe" style:
  ASSERT_DEATH(ThisShouldDie(), "");
}

TEST(MyDeathTest, TestTwo) {
  // This test is run in the "fast" style:
  ASSERT_DEATH(ThisShouldDie(), "");
}
```

### Caveats

The `statement` argument of `ASSERT_EXIT()` can be any valid C++ statement. If
it leaves the current function via a `return` statement or by throwing an
exception, the death test is considered to have failed. Some googletest macros
may return from the current function (e.g. `ASSERT_TRUE()`), so be sure to avoid
them in `statement`.

Since `statement` runs in the child process, any in-memory side effect (e.g.
modifying a variable, releasing memory, etc) it causes will *not* be observable
in the parent process. In particular, if you release memory in a death test,
your program will fail the heap check as the parent process will never see the
memory reclaimed. To solve this problem, you can

1.  try not to free memory in a death test;
2.  free the memory again in the parent process; or
3.  do not use the heap checker in your program.

Due to an implementation detail, you cannot place multiple death test assertions
on the same line; otherwise, compilation will fail with an unobvious error
message.

Despite the improved thread safety afforded by the "threadsafe" style of death
test, thread problems such as deadlock are still possible in the presence of
handlers registered with `pthread_atfork(3)`.


## Using Assertions in Sub-routines

### Adding Traces to Assertions

If a test sub-routine is called from several places, when an assertion inside it
fails, it can be hard to tell which invocation of the sub-routine the failure is
from. You can alleviate this problem using extra logging or custom failure
messages, but that usually clutters up your tests. A better solution is to use
the `SCOPED_TRACE` macro or the `ScopedTrace` utility:

```c++
SCOPED_TRACE(message);
```
```c++
ScopedTrace trace("file_path", line_number, message);
```

where `message` can be anything streamable to `std::ostream`. `SCOPED_TRACE`
macro will cause the current file name, line number, and the given message to be
added in every failure message. `ScopedTrace` accepts explicit file name and
line number in arguments, which is useful for writing test helpers. The effect
will be undone when the control leaves the current lexical scope.

For example,

```c++
10: void Sub1(int n) {
11:   EXPECT_EQ(Bar(n), 1);
12:   EXPECT_EQ(Bar(n + 1), 2);
13: }
14:
15: TEST(FooTest, Bar) {
16:   {
17:     SCOPED_TRACE("A");  // This trace point will be included in
18:                         // every failure in this scope.
19:     Sub1(1);
20:   }
21:   // Now it won't.
22:   Sub1(9);
23: }
```

could result in messages like these:

```none
path/to/foo_test.cc:11: Failure
Value of: Bar(n)
Expected: 1
  Actual: 2
Google Test trace:
path/to/foo_test.cc:17: A

path/to/foo_test.cc:12: Failure
Value of: Bar(n + 1)
Expected: 2
  Actual: 3
```

Without the trace, it would've been difficult to know which invocation of
`Sub1()` the two failures come from respectively. (You could add an extra
message to each assertion in `Sub1()` to indicate the value of `n`, but that's
tedious.)

Some tips on using `SCOPED_TRACE`:

1.  With a suitable message, it's often enough to use `SCOPED_TRACE` at the
    beginning of a sub-routine, instead of at each call site.
2.  When calling sub-routines inside a loop, make the loop iterator part of the
    message in `SCOPED_TRACE` such that you can know which iteration the failure
    is from.
3.  Sometimes the line number of the trace point is enough for identifying the
    particular invocation of a sub-routine. In this case, you don't have to
    choose a unique message for `SCOPED_TRACE`. You can simply use `""`.
4.  You can use `SCOPED_TRACE` in an inner scope when there is one in the outer
    scope. In this case, all active trace points will be included in the failure
    messages, in reverse order they are encountered.
5.  The trace dump is clickable in Emacs - hit `return` on a line number and
    you'll be taken to that line in the source file!

### Propagating Fatal Failures

A common pitfall when using `ASSERT_*` and `FAIL*` is not understanding that
when they fail they only abort the _current function_, not the entire test. For
example, the following test will segfault:

```c++
void Subroutine() {
  // Generates a fatal failure and aborts the current function.
  ASSERT_EQ(1, 2);

  // The following won't be executed.
  ...
}

TEST(FooTest, Bar) {
  Subroutine();  // The intended behavior is for the fatal failure
                 // in Subroutine() to abort the entire test.

  // The actual behavior: the function goes on after Subroutine() returns.
  int* p = NULL;
  *p = 3;  // Segfault!
}
```

To alleviate this, googletest provides three different solutions. You could use
either exceptions, the `(ASSERT|EXPECT)_NO_FATAL_FAILURE` assertions or the
`HasFatalFailure()` function. They are described in the following two
subsections.

#### Asserting on Subroutines with an exception

The following code can turn ASSERT-failure into an exception:

```c++
class ThrowListener : public testing::EmptyTestEventListener {
  void OnTestPartResult(const testing::TestPartResult& result) override {
    if (result.type() == testing::TestPartResult::kFatalFailure) {
      throw testing::AssertionException(result);
    }
  }
};
int main(int argc, char** argv) {
  ...
  testing::UnitTest::GetInstance()->listeners().Append(new ThrowListener);
  return RUN_ALL_TESTS();
}
```

This listener should be added after other listeners if you have any, otherwise
they won't see failed `OnTestPartResult`.

#### Asserting on Subroutines

As shown above, if your test calls a subroutine that has an `ASSERT_*` failure
in it, the test will continue after the subroutine returns. This may not be what
you want.

Often people want fatal failures to propagate like exceptions. For that
googletest offers the following macros:

Fatal assertion                       | Nonfatal assertion                    | Verifies
------------------------------------- | ------------------------------------- | --------
`ASSERT_NO_FATAL_FAILURE(statement);` | `EXPECT_NO_FATAL_FAILURE(statement);` | `statement` doesn't generate any new fatal failures in the current thread.

Only failures in the thread that executes the assertion are checked to determine
the result of this type of assertions. If `statement` creates new threads,
failures in these threads are ignored.

Examples:

```c++
ASSERT_NO_FATAL_FAILURE(Foo());

int i;
EXPECT_NO_FATAL_FAILURE({
  i = Bar();
});
```

Assertions from multiple threads are currently not supported on Windows.

#### Checking for Failures in the Current Test

`HasFatalFailure()` in the `::testing::Test` class returns `true` if an
assertion in the current test has suffered a fatal failure. This allows
functions to catch fatal failures in a sub-routine and return early.

```c++
class Test {
 public:
  ...
  static bool HasFatalFailure();
};
```

The typical usage, which basically simulates the behavior of a thrown exception,
is:

```c++
TEST(FooTest, Bar) {
  Subroutine();
  // Aborts if Subroutine() had a fatal failure.
  if (HasFatalFailure()) return;

  // The following won't be executed.
  ...
}
```

If `HasFatalFailure()` is used outside of `TEST()` , `TEST_F()` , or a test
fixture, you must add the `::testing::Test::` prefix, as in:

```c++
if (::testing::Test::HasFatalFailure()) return;
```

Similarly, `HasNonfatalFailure()` returns `true` if the current test has at
least one non-fatal failure, and `HasFailure()` returns `true` if the current
test has at least one failure of either kind.

## Logging Additional Information

In your test code, you can call `RecordProperty("key", value)` to log additional
information, where `value` can be either a string or an `int`. The *last* value
recorded for a key will be emitted to the
[XML output](#generating-an-xml-report) if you specify one. For example, the
test

```c++
TEST_F(WidgetUsageTest, MinAndMaxWidgets) {
  RecordProperty("MaximumWidgets", ComputeMaxUsage());
  RecordProperty("MinimumWidgets", ComputeMinUsage());
}
```

will output XML like this:

```xml
  ...
    <testcase name="MinAndMaxWidgets" status="run" time="0.006" classname="WidgetUsageTest" MaximumWidgets="12" MinimumWidgets="9" />
  ...
```

> NOTE:
>
> *   `RecordProperty()` is a static member of the `Test` class. Therefore it
>     needs to be prefixed with `::testing::Test::` if used outside of the
>     `TEST` body and the test fixture class.
> *   *`key`* must be a valid XML attribute name, and cannot conflict with the
>     ones already used by googletest (`name`, `status`, `time`, `classname`,
>     `type_param`, and `value_param`).
> *   Calling `RecordProperty()` outside of the lifespan of a test is allowed.
>     If it's called outside of a test but between a test suite's
>     `SetUpTestSuite()` and `TearDownTestSuite()` methods, it will be
>     attributed to the XML element for the test suite. If it's called outside
>     of all test suites (e.g. in a test environment), it will be attributed to
>     the top-level XML element.

## Sharing Resources Between Tests in the Same Test Suite

googletest creates a new test fixture object for each test in order to make
tests independent and easier to debug. However, sometimes tests use resources
that are expensive to set up, making the one-copy-per-test model prohibitively
expensive.

If the tests don't change the resource, there's no harm in their sharing a
single resource copy. So, in addition to per-test set-up/tear-down, googletest
also supports per-test-suite set-up/tear-down. To use it:

1.  In your test fixture class (say `FooTest` ), declare as `static` some member
    variables to hold the shared resources.
2.  Outside your test fixture class (typically just below it), define those
    member variables, optionally giving them initial values.
3.  In the same test fixture class, define a `static void SetUpTestSuite()`
    function (remember not to spell it as **`SetupTestSuite`** with a small
    `u`!) to set up the shared resources and a `static void TearDownTestSuite()`
    function to tear them down.

That's it! googletest automatically calls `SetUpTestSuite()` before running the
*first test* in the `FooTest` test suite (i.e. before creating the first
`FooTest` object), and calls `TearDownTestSuite()` after running the *last test*
in it (i.e. after deleting the last `FooTest` object). In between, the tests can
use the shared resources.

Remember that the test order is undefined, so your code can't depend on a test
preceding or following another. Also, the tests must either not modify the state
of any shared resource, or, if they do modify the state, they must restore the
state to its original value before passing control to the next test.

Here's an example of per-test-suite set-up and tear-down:

```c++
class FooTest : public ::testing::Test {
 protected:
  // Per-test-suite set-up.
  // Called before the first test in this test suite.
  // Can be omitted if not needed.
  static void SetUpTestSuite() {
    shared_resource_ = new ...;
  }

  // Per-test-suite tear-down.
  // Called after the last test in this test suite.
  // Can be omitted if not needed.
  static void TearDownTestSuite() {
    delete shared_resource_;
    shared_resource_ = NULL;
  }

  // You can define per-test set-up logic as usual.
  virtual void SetUp() { ... }

  // You can define per-test tear-down logic as usual.
  virtual void TearDown() { ... }

  // Some expensive resource shared by all tests.
  static T* shared_resource_;
};

T* FooTest::shared_resource_ = NULL;

TEST_F(FooTest, Test1) {
  ... you can refer to shared_resource_ here ...
}

TEST_F(FooTest, Test2) {
  ... you can refer to shared_resource_ here ...
}
```

NOTE: Though the above code declares `SetUpTestSuite()` protected, it may
sometimes be necessary to declare it public, such as when using it with
`TEST_P`.

## Global Set-Up and Tear-Down

Just as you can do set-up and tear-down at the test level and the test suite
level, you can also do it at the test program level. Here's how.

First, you subclass the `::testing::Environment` class to define a test
environment, which knows how to set-up and tear-down:

```c++
class Environment : public ::testing::Environment {
 public:
  ~Environment() override {}

  // Override this to define how to set up the environment.
  void SetUp() override {}

  // Override this to define how to tear down the environment.
  void TearDown() override {}
};
```

Then, you register an instance of your environment class with googletest by
calling the `::testing::AddGlobalTestEnvironment()` function:

```c++
Environment* AddGlobalTestEnvironment(Environment* env);
```

Now, when `RUN_ALL_TESTS()` is called, it first calls the `SetUp()` method of
each environment object, then runs the tests if none of the environments
reported fatal failures and `GTEST_SKIP()` was not called. `RUN_ALL_TESTS()`
always calls `TearDown()` with each environment object, regardless of whether or
not the tests were run.

It's OK to register multiple environment objects. In this suite, their `SetUp()`
will be called in the order they are registered, and their `TearDown()` will be
called in the reverse order.

Note that googletest takes ownership of the registered environment objects.
Therefore **do not delete them** by yourself.

You should call `AddGlobalTestEnvironment()` before `RUN_ALL_TESTS()` is called,
probably in `main()`. If you use `gtest_main`, you need to call this before
`main()` starts for it to take effect. One way to do this is to define a global
variable like this:

```c++
::testing::Environment* const foo_env =
    ::testing::AddGlobalTestEnvironment(new FooEnvironment);
```

However, we strongly recommend you to write your own `main()` and call
`AddGlobalTestEnvironment()` there, as relying on initialization of global
variables makes the code harder to read and may cause problems when you register
multiple environments from different translation units and the environments have
dependencies among them (remember that the compiler doesn't guarantee the order
in which global variables from different translation units are initialized).

## Value-Parameterized Tests

*Value-parameterized tests* allow you to test your code with different
parameters without writing multiple copies of the same test. This is useful in a
number of situations, for example:

*   You have a piece of code whose behavior is affected by one or more
    command-line flags. You want to make sure your code performs correctly for
    various values of those flags.
*   You want to test different implementations of an OO interface.
*   You want to test your code over various inputs (a.k.a. data-driven testing).
    This feature is easy to abuse, so please exercise your good sense when doing
    it!

### How to Write Value-Parameterized Tests

To write value-parameterized tests, first you should define a fixture class. It
must be derived from both `testing::Test` and `testing::WithParamInterface<T>`
(the latter is a pure interface), where `T` is the type of your parameter
values. For convenience, you can just derive the fixture class from
`testing::TestWithParam<T>`, which itself is derived from both `testing::Test`
and `testing::WithParamInterface<T>`. `T` can be any copyable type. If it's a
raw pointer, you are responsible for managing the lifespan of the pointed
values.

NOTE: If your test fixture defines `SetUpTestSuite()` or `TearDownTestSuite()`
they must be declared **public** rather than **protected** in order to use
`TEST_P`.

```c++
class FooTest :
    public testing::TestWithParam<const char*> {
  // You can implement all the usual fixture class members here.
  // To access the test parameter, call GetParam() from class
  // TestWithParam<T>.
};

// Or, when you want to add parameters to a pre-existing fixture class:
class BaseTest : public testing::Test {
  ...
};
class BarTest : public BaseTest,
                public testing::WithParamInterface<const char*> {
  ...
};
```

Then, use the `TEST_P` macro to define as many test patterns using this fixture
as you want. The `_P` suffix is for "parameterized" or "pattern", whichever you
prefer to think.

```c++
TEST_P(FooTest, DoesBlah) {
  // Inside a test, access the test parameter with the GetParam() method
  // of the TestWithParam<T> class:
  EXPECT_TRUE(foo.Blah(GetParam()));
  ...
}

TEST_P(FooTest, HasBlahBlah) {
  ...
}
```

Finally, you can use `INSTANTIATE_TEST_SUITE_P` to instantiate the test suite
with any set of parameters you want. googletest defines a number of functions
for generating test parameters. They return what we call (surprise!) *parameter
generators*. Here is a summary of them, which are all in the `testing`
namespace:

<!-- mdformat off(github rendering does not support multiline tables) -->

| Parameter Generator                                                                       | Behavior                                                                                                          |
| ----------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------- |
| `Range(begin, end [, step])`                                                              | Yields values `{begin, begin+step, begin+step+step, ...}`. The values do not include `end`. `step` defaults to 1. |
| `Values(v1, v2, ..., vN)`                                                                 | Yields values `{v1, v2, ..., vN}`.                                                                                |
| `ValuesIn(container)` and  `ValuesIn(begin,end)`                                          | Yields values from a C-style array, an  STL-style container, or an iterator range `[begin, end)`                  |
| `Bool()`                                                                                  | Yields sequence `{false, true}`.                                                                                  |
| `Combine(g1, g2, ..., gN)`                                                                | Yields all combinations (Cartesian product) as std\:\:tuples of the values generated by the `N` generators.       |

<!-- mdformat on-->

For more details, see the comments at the definitions of these functions.

The following statement will instantiate tests from the `FooTest` test suite
each with parameter values `"meeny"`, `"miny"`, and `"moe"`.