Add a test of CheckUniqueFilenames

2 files changed, 38 insertions, 4 deletions

diff --git a/tests/helpers.py b/tests/helpers.py
index ebc15cd1..a132872e 100644
--- a/tests/helpers.py
+++ b/tests/helpers.py
@@ -54,11 +54,19 @@ class CheckUniqueFilenames(object):
         self.wrapped = wrapped
 
     @classmethod
-    def hook(cls, cov, method_name):
-        """Replace a method with our checking wrapper."""
-        method = getattr(cov, method_name)
+    def hook(cls, obj, method_name):
+        """Replace a method with our checking wrapper.
+
+        The method must take a string as a first argument. That argument
+        will be checked for uniqueness across all the calls to this method.
+
+        The values don't have to be file names actually, just strings, but
+        we only use it for filename arguments.
+
+        """
+        method = getattr(obj, method_name)
         hook = cls(method)
-        setattr(cov, method_name, hook.wrapper)
+        setattr(obj, method_name, hook.wrapper)
         return hook
 
     def wrapper(self, filename, *args, **kwargs):
diff --git a/tests/test_testing.py b/tests/test_testing.py
index d91de28d..d0e75797 100644
--- a/tests/test_testing.py
+++ b/tests/test_testing.py
@@ -13,6 +13,7 @@ from coverage.backunittest import TestCase
 from coverage.files import actual_path
 
 from tests.coveragetest import CoverageTest
+from tests.helpers import CheckUniqueFilenames
 
 
 class TestingTest(TestCase):
@@ -140,6 +141,31 @@ class CoverageTestTest(CoverageTest):
         self.assertEqual(environ.strip(), "COV_FOOBAR = XYZZY")
 
 
+class CheckUniqueFilenamesTest(CoverageTest):
+    """Tests of CheckUniqueFilenames."""
+
+    class Stub(object):
+        """A stand-in for the class we're checking."""
+        def __init__(self, x):
+            self.x = x
+
+        def method(self, filename, a=17, b="hello"):
+            """The method we'll wrap, with args to be sure args work."""
+            return (self.x, filename, a, b)
+
+    def test_detect_duplicate(self):
+        stub = self.Stub(23)
+        CheckUniqueFilenames.hook(stub, "method")
+
+        # Two method calls with different names are fine.
+        assert stub.method("file1") == (23, "file1", 17, "hello")
+        assert stub.method("file2", 1723, b="what") == (23, "file2", 1723, "what")
+
+        # A duplicate file name trips an assertion.
+        with self.assertRaises(AssertionError):
+            stub.method("file1")
+
+
 def same_python_executable(e1, e2):
     """Determine if `e1` and `e2` refer to the same Python executable.