[Extern Generation] Add a presubmit script to check externs not being updated

extensions/common/api/externs_checker_test.py

Index: extensions/common/api/externs_checker_test.py
diff --git a/extensions/common/api/externs_checker_test.py b/extensions/common/api/externs_checker_test.py
new file mode 100755
index 0000000000000000000000000000000000000000..73b65fa3c06266487bd14780d702d115f14962ed
--- /dev/null
+++ b/extensions/common/api/externs_checker_test.py
@@ -0,0 +1,63 @@
+#!/usr/bin/env python
+# 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 os
+import sys
+import unittest
+
+from externs_checker import ExternsChecker
+
+sys.path.append(
+    os.path.join(os.path.dirname(os.path.abspath(__file__)), '..', '..', '..'))
+
+from PRESUBMIT_test_mocks import MockInputApi, MockOutputApi, MockFile
+
+
+class ExternsCheckerTest(unittest.TestCase):
+  API_PAIRS = {'a': '1', 'b': '2', 'c': '3'}
+
+  def _runChecks(self, files):
+    input_api = MockInputApi()
+    input_api.files = [MockFile(f, '') for f in files]
+    output_api = MockOutputApi()
+    checker = ExternsChecker(input_api, output_api, self.API_PAIRS)
+    return checker.RunChecks()
+
+  def testModifiedSourceWithoutModifiedExtern(self):
+    results = self._runChecks(['b', 'test', 'random'])
+    self.assertEquals(1, len(results))
+    self.assertEquals(1, len(results[0].items))
+    self.assertEquals('b', results[0].items[0])
+    self.assertEquals(
+        'To update the externs, run:\n'
+        ' src/ $ python tools/json_schema_compiler/compiler.py b --root=. '
+        '--generator=externs > 2',
+        results[0].long_text)
+
+  def testModifiedSourceWithModifiedExtern(self):
+    results = self._runChecks(['b', '2', 'test', 'random'])
+    self.assertEquals(0, len(results))
+
+  def testModifiedMultipleSourcesWithNoModifiedExterns(self):
+    results = self._runChecks(['b', 'test', 'c', 'random'])
+    self.assertEquals(1, len(results))
+    self.assertEquals(2, len(results[0].items))
+    self.assertTrue('b' in results[0].items)
+    self.assertTrue('c' in results[0].items)
+    self.assertEquals(
+        'To update the externs, run:\n'
+        ' src/ $ python tools/json_schema_compiler/compiler.py <source_file> '
+        '--root=. --generator=externs > <output_file>',
+        results[0].long_text)
+
+  def testModifiedMultipleSourcesWithOneModifiedExtern(self):
+    results = self._runChecks(['b', 'test', 'c', 'random', '2'])
+    self.assertEquals(1, len(results))
+    self.assertEquals(1, len(results[0].items))
+    self.assertEquals('c', results[0].items[0])
+
+
+if __name__ == '__main__':
+  unittest.main()