Implement merge-files only using @bukzor's method.

tests/git_test.py

@@ -14,6 +14,14 @@ def test_get_root(empty_git_dir):
         assert git.get_root() == empty_git_dir
 
 
+def test_is_in_merge_conflict(empty_git_dir):
+    assert git.is_in_merge_conflict() is False
+
+
+def test_is_not_in_merge_conflict(in_merge_conflict):
+    assert git.is_in_merge_conflict() is True
+
+
 @pytest.fixture
 def get_files_matching_func():
     def get_filenames():
@@ -57,3 +65,48 @@ def test_does_not_include_deleted_fileS(get_files_matching_func):
 def test_exclude_removes_files(get_files_matching_func):
     ret = get_files_matching_func('', '\\.py$')
     assert ret == set(['hooks.yaml'])
+
+
+def resolve_conflict():
+    with open('conflict_file', 'w') as conflicted_file:
+        conflicted_file.write('herp\nderp\n')
+    local['git']['add', 'conflict_file']()
+
+
+def test_get_conflicted_files(in_merge_conflict):
+    resolve_conflict()
+    with open('other_file', 'w') as other_file:
+        other_file.write('oh hai')
+    local['git']['add', 'other_file']()
+
+    ret = set(git.get_conflicted_files())
+    assert ret == set(('conflict_file', 'other_file'))
+
+
+def test_get_conflicted_files_unstaged_files(in_merge_conflict):
+    # If they for whatever reason did pre-commit run --no-stash during a
+    # conflict
+    resolve_conflict()
+
+    # Make unstaged file.
+    with open('bar_only_file', 'w') as bar_only_file:
+        bar_only_file.write('new contents!\n')
+
+    ret = set(git.get_conflicted_files())
+    assert ret == set(('conflict_file',))
+
+
+MERGE_MSG = "Merge branch 'foo' into bar\n\nConflicts:\n\tconflict_file\n"
+OTHER_MERGE_MSG = MERGE_MSG + '\tother_conflict_file\n'
+
+
+@pytest.mark.parametrize(
+    ('input', 'expected_output'),
+    (
+        (MERGE_MSG, ['conflict_file']),
+        (OTHER_MERGE_MSG, ['conflict_file', 'other_conflict_file']),
+    ),
+)
+def test_parse_merge_msg_for_conflicts(input, expected_output):
+    ret = git.parse_merge_msg_for_conflicts(input)
+    assert ret == expected_output