1 files changed, 25 insertions, 0 deletions
diff --git a/tests/helpers.py b/tests/helpers.py
new file mode 100644
index 00000000..db20d798
--- /dev/null
+++ b/tests/helpers.py
@@ -0,0 +1,25 @@
+"""Helpers for coverage.py tests."""
+
+
+class CheckUniqueFilenames(object):
+    """Asserts the uniqueness of filenames passed to a function."""
+    def __init__(self, wrapped):
+        self.filenames = set()
+        self.wrapped = wrapped
+
+    @classmethod
+    def hook(cls, cov, method_name):
+        """Replace a method with our checking wrapper."""
+        method = getattr(cov, method_name)
+        hook = cls(method)
+        setattr(cov, method_name, hook.wrapper)
+        return hook
+
+    def wrapper(self, filename, *args, **kwargs):
+        """The replacement method.  Check that we don't have dupes."""
+        assert filename not in self.filenames, (
+            "Filename %r passed to %r twice" % (filename, self.wrapped)
+            )
+        self.filenames.add(filename)
+        ret = self.wrapped(filename, *args, **kwargs)
+        return ret