Change ChromiumCommit.format_patch to use a filtered list of files

third_party/WebKit/Tools/Scripts/webkitpy/w3c/chromium_commit_unittest.py

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import unittest
 from webkitpy.common.host_mock import MockHost
 from webkitpy.common.system.executive_mock import MockExecutive2
 from webkitpy.w3c.chromium_commit import ChromiumCommit
+from webkitpy.w3c.test_exporter import CHROMIUM_WPT_DIR
+from webkitpy.w3c.test_exporter_unittest import mock_command_exec
 
 
 class ChromiumCommitTest(unittest.TestCase):
 
     def test_accepts_sha(self):
         chromium_commit = ChromiumCommit(MockHost(), sha='deadbeefcafe')
 
         self.assertEqual(chromium_commit.sha, 'deadbeefcafe')
         self.assertIsNone(chromium_commit.position)
 
     def test_derives_sha_from_position(self):
         host = MockHost()
         host.executive = MockExecutive2(output='deadbeefcafe')
         pos = 'Cr-Commit-Position: refs/heads/master@{#789}'
         chromium_commit = ChromiumCommit(host, position=pos)
 
         self.assertEqual(chromium_commit.position, 'refs/heads/master@{#789}')
         self.assertEqual(chromium_commit.sha, 'deadbeefcafe')
+
+    def test_filtered_changed_files_blacklist(self):
+        host = MockHost()
+
+        fake_files = ['file1', 'MANIFEST.json', 'file3']
+        qualified_fake_files = [CHROMIUM_WPT_DIR + f for f in fake_files]
+
+        host.executive = mock_command_exec({
+            'diff-tree': '\n'.join(qualified_fake_files),
+            'crrev-parse': 'fake rev',
+        })
+
+        pos = 'Cr-Commit-Position: refs/heads/master@{#789}'

[qyearsley, 2016/12/21 00:24:46]

Nit: if you want to avoid abbreviation variable names, this could be
position_string.

[jeffcarp, 2016/12/21 19:12:52]

Done, abbreviated variables begone! I chose to name it position_footer because
putting the variable type in variables makes me feel kind of weird for reasons I
can't accurately describe.

[qyearsley, 2016/12/21 19:19:56]

Yeah -- the main reason I've heard before is that in statically-typed languages,
putting the type in the variable name is redundant, e.g. in C++ if you used
`std::string position_string` you would just be repeating yourself.

But even in Python, the type of the variable should be obvious, especially in
this case.

I think the reason why I didn't suggest "position", is that "commit position"
has a very more specific meaning elsewhere: it has to be just the
"refs/heads/master@{#789}" part, including the ref and number, and nothing else.

position_footer is definitely the best variable name here.

+        chromium_commit = ChromiumCommit(host, position=pos)
+
+        files = chromium_commit.filtered_changed_files()
+
+        expected_files = ['file1', 'file3']
+        qualified_expected_files = [CHROMIUM_WPT_DIR + f for f in expected_files]
+
+        self.assertEqual(files, qualified_expected_files)