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|
Please send your questions to the
[googlemock](http://groups.google.com/group/googlemock) discussion
group. If you need help with compiler errors, make sure you have
tried [Google Mock Doctor](#How_am_I_supposed_to_make_sense_of_these_horrible_template_error.md) first.
## When I call a method on my mock object, the method for the real object is invoked instead. What's the problem? ##
In order for a method to be mocked, it must be _virtual_, unless you use the [high-perf dependency injection technique](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Mocking_Nonvirtual_Methods).
## I wrote some matchers. After I upgraded to a new version of Google Mock, they no longer compile. What's going on? ##
After version 1.4.0 of Google Mock was released, we had an idea on how
to make it easier to write matchers that can generate informative
messages efficiently. We experimented with this idea and liked what
we saw. Therefore we decided to implement it.
Unfortunately, this means that if you have defined your own matchers
by implementing `MatcherInterface` or using `MakePolymorphicMatcher()`,
your definitions will no longer compile. Matchers defined using the
`MATCHER*` family of macros are not affected.
Sorry for the hassle if your matchers are affected. We believe it's
in everyone's long-term interest to make this change sooner than
later. Fortunately, it's usually not hard to migrate an existing
matcher to the new API. Here's what you need to do:
If you wrote your matcher like this:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MatcherInterface;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
...
};
```
you'll need to change it to:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MatcherInterface;
using ::testing::MatchResultListener;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
...
};
```
(i.e. rename `Matches()` to `MatchAndExplain()` and give it a second
argument of type `MatchResultListener*`.)
If you were also using `ExplainMatchResultTo()` to improve the matcher
message:
```
// Old matcher definition that doesn't work with the lastest
// Google Mock.
using ::testing::MatcherInterface;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetFoo() > 5;
}
virtual void ExplainMatchResultTo(MyType value,
::std::ostream* os) const {
// Prints some helpful information to os to help
// a user understand why value matches (or doesn't match).
*os << "the Foo property is " << value.GetFoo();
}
...
};
```
you should move the logic of `ExplainMatchResultTo()` into
`MatchAndExplain()`, using the `MatchResultListener` argument where
the `::std::ostream` was used:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MatcherInterface;
using ::testing::MatchResultListener;
...
class MyWonderfulMatcher : public MatcherInterface<MyType> {
public:
...
virtual bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
*listener << "the Foo property is " << value.GetFoo();
return value.GetFoo() > 5;
}
...
};
```
If your matcher is defined using `MakePolymorphicMatcher()`:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MakePolymorphicMatcher;
...
class MyGreatMatcher {
public:
...
bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
you should rename the `Matches()` method to `MatchAndExplain()` and
add a `MatchResultListener*` argument (the same as what you need to do
for matchers defined by implementing `MatcherInterface`):
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MakePolymorphicMatcher;
using ::testing::MatchResultListener;
...
class MyGreatMatcher {
public:
...
bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
If your polymorphic matcher uses `ExplainMatchResultTo()` for better
failure messages:
```
// Old matcher definition that doesn't work with the latest
// Google Mock.
using ::testing::MakePolymorphicMatcher;
...
class MyGreatMatcher {
public:
...
bool Matches(MyType value) const {
// Returns true if value matches.
return value.GetBar() < 42;
}
...
};
void ExplainMatchResultTo(const MyGreatMatcher& matcher,
MyType value,
::std::ostream* os) {
// Prints some helpful information to os to help
// a user understand why value matches (or doesn't match).
*os << "the Bar property is " << value.GetBar();
}
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
you'll need to move the logic inside `ExplainMatchResultTo()` to
`MatchAndExplain()`:
```
// New matcher definition that works with the latest Google Mock.
using ::testing::MakePolymorphicMatcher;
using ::testing::MatchResultListener;
...
class MyGreatMatcher {
public:
...
bool MatchAndExplain(MyType value,
MatchResultListener* listener) const {
// Returns true if value matches.
*listener << "the Bar property is " << value.GetBar();
return value.GetBar() < 42;
}
...
};
... MakePolymorphicMatcher(MyGreatMatcher()) ...
```
For more information, you can read these
[two](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Writing_New_Monomorphic_Matchers)
[recipes](http://code.google.com/p/googlemock/wiki/V1_6_CookBook#Writing_New_Polymorphic_Matchers)
from the cookbook. As always, you
are welcome to post questions on `googlemock@googlegroups.com` if you
need any help.
## When using Google Mock, do I have to use Google Test as the testing framework? I have my favorite testing framework and don't want to switch. ##
Google Mock works out of the box with Google Test. However, it's easy
to configure it to work with any testing framework of your choice.
[Here](http://code.google.com/p/googlemock/wiki/V1_6_ForDummies#Using_Google_Mock_with_Any_Testing_Framework) is how.
## How am I supposed to make sense of these horrible template errors? ##
If you are confused by the compiler errors gcc threw at you,
try consulting the _Google Mock Doctor_ tool first. What it does is to
scan stdin for gcc error messages, and spit out diagnoses on the
problems (we call them diseases) your code has.
To "install", run command:
```
alias gmd='<path to googlemock>/scripts/gmock_doctor.py'
```
To use it, do:
```
<your-favorite-build-command> <your-test> 2>&1 | gmd
```
For example:
```
make my_test 2>&1 | gmd
```
Or you can run `gmd` and copy-n-paste gcc's error messages to it.
## Can I mock a variadic function? ##
You cannot mock a variadic function (i.e. a function taking ellipsis
(`...`) arguments) directly in Google Mock.
The problem is that in general, there is _no way_ for a mock object to
know how many arguments are passed to the variadic method, and what
the arguments' types are. Only the _author of the base class_ knows
the protocol, and we cannot look into his head.
Therefore, to mock such a function, the _user_ must teach the mock
object how to figure out the number of arguments and their types. One
way to do it is to provide overloaded versions of the function.
Ellipsis arguments are inherited from C and not really a C++ feature.
They are unsafe to use and don't work with arguments that have
constructors or destructors. Therefore we recommend to avoid them in
C++ as much as possible.
## MSVC gives me warning C4301 or C4373 when I define a mock method with a const parameter. Why? ##
If you compile this using Microsoft Visual C++ 2005 SP1:
```
class Foo {
...
virtual void Bar(const int i) = 0;
};
class MockFoo : public Foo {
...
MOCK_METHOD1(Bar, void(const int i));
};
```
You may get the following warning:
```
warning C4301: 'MockFoo::Bar': overriding virtual function only differs from 'Foo::Bar' by const/volatile qualifier
```
This is a MSVC bug. The same code compiles fine with gcc ,for
example. If you use Visual C++ 2008 SP1, you would get the warning:
```
warning C4373: 'MockFoo::Bar': virtual function overrides 'Foo::Bar', previous versions of the compiler did not override when parameters only differed by const/volatile qualifiers
```
In C++, if you _declare_ a function with a `const` parameter, the
`const` modifier is _ignored_. Therefore, the `Foo` base class above
is equivalent to:
```
class Foo {
...
virtual void Bar(int i) = 0; // int or const int? Makes no difference.
};
```
In fact, you can _declare_ Bar() with an `int` parameter, and _define_
it with a `const int` parameter. The compiler will still match them
up.
Since making a parameter `const` is meaningless in the method
_declaration_, we recommend to remove it in both `Foo` and `MockFoo`.
That should workaround the VC bug.
Note that we are talking about the _top-level_ `const` modifier here.
If the function parameter is passed by pointer or reference, declaring
the _pointee_ or _referee_ as `const` is still meaningful. For
example, the following two declarations are _not_ equivalent:
```
void Bar(int* p); // Neither p nor *p is const.
void Bar(const int* p); // p is not const, but *p is.
```
## I have a huge mock class, and Microsoft Visual C++ runs out of memory when compiling it. What can I do? ##
We've noticed that when the `/clr` compiler flag is used, Visual C++
uses 5~6 times as much memory when compiling a mock class. We suggest
to avoid `/clr` when compiling native C++ mocks.
## I can't figure out why Google Mock thinks my expectations are not satisfied. What should I do? ##
You might want to run your test with
`--gmock_verbose=info`. This flag lets Google Mock print a trace
of every mock function call it receives. By studying the trace,
you'll gain insights on why the expectations you set are not met.
## How can I assert that a function is NEVER called? ##
```
EXPECT_CALL(foo, Bar(_))
.Times(0);
```
## I have a failed test where Google Mock tells me TWICE that a particular expectation is not satisfied. Isn't this redundant? ##
When Google Mock detects a failure, it prints relevant information
(the mock function arguments, the state of relevant expectations, and
etc) to help the user debug. If another failure is detected, Google
Mock will do the same, including printing the state of relevant
expectations.
Sometimes an expectation's state didn't change between two failures,
and you'll see the same description of the state twice. They are
however _not_ redundant, as they refer to _different points in time_.
The fact they are the same _is_ interesting information.
## I get a heap check failure when using a mock object, but using a real object is fine. What can be wrong? ##
Does the class (hopefully a pure interface) you are mocking have a
virtual destructor?
Whenever you derive from a base class, make sure its destructor is
virtual. Otherwise Bad Things will happen. Consider the following
code:
```
class Base {
public:
// Not virtual, but should be.
~Base() { ... }
...
};
class Derived : public Base {
public:
...
private:
std::string value_;
};
...
Base* p = new Derived;
...
delete p; // Surprise! ~Base() will be called, but ~Derived() will not
// - value_ is leaked.
```
By changing `~Base()` to virtual, `~Derived()` will be correctly
called when `delete p` is executed, and the heap checker
will be happy.
## The "newer expectations override older ones" rule makes writing expectations awkward. Why does Google Mock do that? ##
When people complain about this, often they are referring to code like:
```
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time. However, I have to write the expectations in the
// reverse order. This sucks big time!!!
EXPECT_CALL(foo, Bar())
.WillOnce(Return(2))
.RetiresOnSaturation();
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.RetiresOnSaturation();
```
The problem is that they didn't pick the **best** way to express the test's
intent.
By default, expectations don't have to be matched in _any_ particular
order. If you want them to match in a certain order, you need to be
explicit. This is Google Mock's (and jMock's) fundamental philosophy: it's
easy to accidentally over-specify your tests, and we want to make it
|
