support --backend as a pytest flag to limit to one backend for testing

1 files changed, 22 insertions, 1 deletions

diff --git a/tests/test_utils.py b/tests/test_utils.py
index e3e53d63..e8037c1d 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -21,7 +21,7 @@ import pytest
 from .utils import (
     load_nist_vectors, load_vectors_from_file, load_cryptrec_vectors,
     load_openssl_vectors, load_hash_vectors, check_for_iface,
-    check_backend_support
+    check_backend_support, modify_backend_list
 )
 
 
@@ -29,6 +29,27 @@ class FakeInterface(object):
     pass
 
 
+def test_modify_backend_list_leave_one():
+    b1 = pretend.stub(name="b1")
+    b2 = pretend.stub(name="b2")
+    b3 = pretend.stub(name="b3")
+    backends = [b1, b2, b3]
+    name = "b2"
+    modify_backend_list(name, backends)
+    assert len(backends) == 1
+    assert backends[0] == b2
+
+
+def test_modify_backend_list_error_none():
+    b1 = pretend.stub(name="b1")
+    b2 = pretend.stub(name="b2")
+    b3 = pretend.stub(name="b3")
+    backends = [b1, b2, b3]
+    name = "back!"
+    with pytest.raises(ValueError):
+        modify_backend_list(name, backends)
+
+
 def test_check_for_iface():
     item = pretend.stub(keywords=["fake_name"], funcargs={"backend": True})
     with pytest.raises(pytest.skip.Exception) as exc_info: