Give a reasonable warning for a previous assert. Closes #353.

3 files changed, 37 insertions, 6 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index aaf2da7b..b0004b5c 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -3,6 +3,15 @@ Change history for Coverage.py
 ------------------------------
 
 
+Latest
+------
+
+- A new warning is possible, if a desired file isn't measure because it was
+  imported before coverage was started (`issue 353`_).
+
+.. _issue 353: https://bitbucket.org/ned/coveragepy/issue/353/40a3-introduces-an-unexpected-third-case
+
+
 Version 4.0a4 --- 25 January 2015
 ---------------------------------
 
diff --git a/coverage/control.py b/coverage/control.py
index 197a7c1e..319f56dc 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -722,12 +722,9 @@ class Coverage(object):
                 ):
                     self._warn("Module %s has no Python source." % pkg)
                 else:
-                    raise AssertionError(
-                        "Unexpected third case: name = %s, "
-                        "object = %r, "
-                        "__file__ = %s" % (
-                            pkg, sys.modules[pkg], sys.modules[pkg].__file__
-                        )
+                    self._warn(
+                        "Module %s was previously imported, "
+                        "but not measured." % pkg
                     )
 
         # Find out if we got any data.
diff --git a/tests/test_process.py b/tests/test_process.py
index a1c853d1..43fdc1bd 100644
--- a/tests/test_process.py
+++ b/tests/test_process.py
@@ -568,6 +568,31 @@ class ProcessTest(CoverageTest):
         out = self.run_command("python allok.py")
         self.assertEqual(out, "No warnings!\n")
 
+    def test_run_twice(self):
+        # https://bitbucket.org/ned/coveragepy/issue/353/40a3-introduces-an-unexpected-third-case
+        self.make_file("foo.py", """\
+            def foo():
+                pass
+            """)
+        self.make_file("run_twice.py", """\
+            import coverage
+
+            for _ in [1, 2]:
+                inst = coverage.Coverage(source=['foo'])
+                inst.load()
+                inst.start()
+                import foo
+                inst.stop()
+                inst.combine()
+                inst.save()
+            """)
+        out = self.run_command("python run_twice.py")
+        self.assertEqual(
+            out,
+            "Coverage.py warning: "
+            "Module foo was previously imported, but not measured.\n"
+        )
+
 
 class AliasedCommandTest(CoverageTest):
     """Tests of the version-specific command aliases."""