Fix blink/PRESUBMIT_test

This test was using mock.py's assert_not_called method but that does
not exist in the version in third_party/pymock. The result is that the
assert call was mocked out, allowing the test to pass without actually
testing anything.

Fix is two-fold:
1 factor out the filtering code and test it directly
2 assert that .call_count is 0

Bug: 890657
Change-Id: Iffc6382ad0d9335a11c17f5ffe4d0c6ae6cbcf6c
Reviewed-on: https://chromium-review.googlesource.com/1253601
Commit-Queue: Fergal Daly <fergal@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595406}

third_party/blink/PRESUBMIT.py

@@ -94,26 +94,34 @@ def _CommonChecks(input_api, output_api):
     return results
 
 
-def _CheckStyle(input_api, output_api):
-    style_checker_path = input_api.os_path.join(input_api.PresubmitLocalPath(),
-                                                'tools', 'check_blink_style.py')
-    args = [input_api.python_executable, style_checker_path, '--diff-files']
+def _FilterPaths(input_api):
+    """Returns input files with certain paths removed."""
     files = []
     for f in input_api.AffectedFiles():
         file_path = f.LocalPath()
-        # Filter out changes in LayoutTests.
-        if 'web_tests' + input_api.os_path.sep in file_path and 'TestExpectations' not in file_path:
+        # Filter out changes in web_tests/.
+        if ('web_tests' + input_api.os_path.sep in file_path
+            and 'TestExpectations' not in file_path):
             continue
         if '/PRESUBMIT' in file_path:
             continue
         files.append(input_api.os_path.join('..', '..', file_path))
+    return files
+
+
+def _CheckStyle(input_api, output_api):
+    files = _FilterPaths(input_api)
     # Do not call check_blink_style.py with empty affected file list if all
     # input_api.AffectedFiles got filtered.
     if not files:
         return []
+
+    style_checker_path = input_api.os_path.join(input_api.PresubmitLocalPath(),
+                                                'tools', 'check_blink_style.py')
+    args = [input_api.python_executable, style_checker_path, '--diff-files']
     args += files
-    results = []
 
+    results = []
     try:
         child = input_api.subprocess.Popen(args,
                                            stderr=input_api.subprocess.PIPE)

third_party/blink/PRESUBMIT_test.py

@@ -70,16 +70,35 @@ class PresubmitTest(unittest.TestCase):
         diff_file_chromium2_h = ['another diff']
         diff_file_layout_test_html = ['more diff']
         mock_input_api = MockInputApi()
-        mock_input_api.files = [
-            MockAffectedFile('first_file_chromium.h', diff_file_chromium1_h),
-            MockAffectedFile('second_file_chromium.h', diff_file_chromium2_h),
-            MockAffectedFile('LayoutTests/some_tests.html', diff_file_layout_test_html)
-        ]
+        mock_input_api.files = []
         # Access to a protected member _CheckStyle
         # pylint: disable=W0212
         PRESUBMIT._CheckStyle(mock_input_api, MockOutputApi())
-        # pylint: disable=E1101
-        subprocess.Popen.assert_not_called()
+        self.assertEqual(0, subprocess.Popen.call_count)
+
+    def test_FilterPaths(self):
+        """This verifies that _FilterPaths removes expected paths."""
+        diff_file_chromium1_h = ['some diff']
+        diff_web_tests_html = ['more diff']
+        diff_presubmit = ['morer diff']
+        diff_test_expectations = ['morest diff']
+        mock_input_api = MockInputApi()
+        mock_input_api.files = [
+            MockAffectedFile('file_chromium1.h', diff_file_chromium1_h),
+            MockAffectedFile('web_tests/some_tests.html', diff_web_tests_html),
+            MockAffectedFile('web_tests/TestExpectations', diff_test_expectations),
+            MockAffectedFile('blink/PRESUBMIT', diff_presubmit),
+        ]
+        # Access to a protected member _FilterPaths
+        # pylint: disable=W0212
+        filtered = PRESUBMIT._FilterPaths(mock_input_api)
+        self.assertEqual(2, len(filtered))
+        self.assertEqual(
+            mock_input_api.os_path.join('..', '..', 'file_chromium1.h'),
+            filtered[0])
+        self.assertEqual(
+            mock_input_api.os_path.join('..', '..', 'web_tests/TestExpectations'),
+            filtered[1])
 
     def testCheckPublicHeaderWithBlinkMojo(self):
         """This verifies that _CheckForWrongMojomIncludes detects -blink mojo