EditCommitMessageAction: New action

A new action for GitCommitBear when applied
opens up a editor for user to edit commit
message of the HEAD commit.

bears/vcs/actions/EditCommitMessageAction.py

@@ -0,0 +1,21 @@
+import subprocess
+from coalib.results.result_actions.ResultAction import ResultAction
+
+
+class EditCommitMessageAction(ResultAction):
+
+    SUCCESS_MESSAGE = 'Commit message edited successfully.'
+
+    @staticmethod
+    def is_applicable(result,
+                      original_file_dict,
+                      file_diff_dict,
+                      applied_actions=()):
+        return True
+
+    def apply(self, result, original_file_dict, file_diff_dict):
+        """
+        Edit (C)ommit Message [Note: This may rewrite your commit history]
+        """
+        subprocess.check_call(['git', 'commit', '-o', '--amend'])
+        return file_diff_dict

tests/vcs/actions/EditCommitMessageActionTest.py

@@ -0,0 +1,24 @@
+import unittest
+from unittest.mock import patch
+from coala_utils.ContextManagers import retrieve_stdout
+from coalib.results.Result import Result
+from bears.vcs.actions.EditCommitMessageAction import EditCommitMessageAction
+
+
+class EditCommitMessageActionTest(unittest.TestCase):
+
+    def setUp(self):
+        self.uut = EditCommitMessageAction()
+        self.result = Result('origin', 'message')
+
+    def test_is_applicable(self):
+        self.assertTrue(self.uut.is_applicable(self.result, {}, {}))
+
+    def test_apply(self):
+        with retrieve_stdout() as stdout:
+            patcher = (
+                'bears.vcs.actions.EditCommitMessageAction.subprocess.check_call')
+            with patch(patcher):
+                ret = self.uut.apply(self.result, {}, {'file': 'diff'})
+                self.assertEqual(ret, {'file': 'diff'})
+                self.assertEqual(stdout.getvalue(), '')