Fix crrev and add test coverage for the main function.

scripts/slave/recipe_modules/crrev/resources/crrev_client_test.py

Index: scripts/slave/recipe_modules/crrev/resources/crrev_client_test.py
diff --git a/scripts/slave/recipe_modules/crrev/resources/crrev_client_test.py b/scripts/slave/recipe_modules/crrev/resources/crrev_client_test.py
index 101a621f576853fa8bc7e76c1c30f4b2e2d08a35..c6631f97e6d2a040e6c3d25062fda22a4b47a36a 100755
--- a/scripts/slave/recipe_modules/crrev/resources/crrev_client_test.py
+++ b/scripts/slave/recipe_modules/crrev/resources/crrev_client_test.py
@@ -22,6 +22,21 @@ import crrev_client  # pylint: disable=relative-import
 @mock.patch('requests.get')
 class CrrevClientTest(unittest.TestCase):
 
+  def test_main(self, mock_get):
+    mock_response = mock.MagicMock()
+    response_data = {
+        'git_sha': 'e91f8875e590ddf00af267062fc1a9ec48658373',
+        'numbering_type': 'COMMIT_POSITION'
+    }
+    mock_response.text = json.dumps(response_data)
+    mock_get.return_value = mock_response
+    output = crrev_client.main([
+        'get_numbering',
+        '--params-file=test_params_file.json',
+    ])
+    self.assertEqual(json.dumps(response_data, indent=2), output)
+    self.assertEqual(mock_get.call_count, 1)
+
   def test_simple_get(self, mock_get):
     mock_response = mock.MagicMock()
     response_data = {