1 files changed, 57 insertions, 0 deletions
diff --git a/tests/test_collector.py b/tests/test_collector.py
new file mode 100644
index 0000000..af3814f
--- /dev/null
+++ b/tests/test_collector.py
@@ -0,0 +1,57 @@
+"""Tests of coverage/collector.py and other collectors."""
+
+import re
+
+import coverage
+from coverage.backward import StringIO
+
+from tests.coveragetest import CoverageTest
+
+
+class CollectorTest(CoverageTest):
+    """Test specific aspects of the collection process."""
+
+    def test_should_trace_cache(self):
+        # The tracers should only invoke should_trace once for each file name.
+        # TODO: Might be better to do this with a mocked _should_trace,
+        # rather than by examining debug output.
+
+        # Make some files that invoke each other.
+        self.make_file("f1.py", """\
+            def f1(x, f):
+                return f(x)
+            """)
+
+        self.make_file("f2.py", """\
+            import f1
+
+            def func(x):
+                return f1.f1(x, otherfunc)
+
+            def otherfunc(x):
+                return x*x
+
+            for i in range(10):
+                func(i)
+            """)
+
+        # Trace one file, but not the other, and get the debug output.
+        debug_out = StringIO()
+        cov = coverage.coverage(
+            include=["f1.py"], debug=['trace'], debug_file=debug_out
+            )
+
+        # Import the python file, executing it.
+        self.start_import_stop(cov, "f2")
+
+        # Grab all the filenames mentioned in debug output, there should be no
+        # duplicates.
+        trace_lines = [
+            l for l in debug_out.getvalue().splitlines()
+            if l.startswith("Tracing ") or l.startswith("Not tracing ")
+        ]
+        filenames = [re.search(r"'[^']+'", l).group() for l in trace_lines]
+        self.assertEqual(len(filenames), len(set(filenames)))
+
+        # Double-check that the tracing messages are in there somewhere.
+        self.assertGreater(len(filenames), 5)