Add check-merge-conflict hook

tests/check_merge_conflict_test.py

@@ -0,0 +1,26 @@
+import os.path
+
+import pytest
+
+from pre_commit_hooks.check_merge_conflict import detect_merge_conflict
+
+# Input, expected return value
+TESTS = (
+    (b'<<<<<<< HEAD', 1),
+    (b'=======', 1),
+    (b'>>>>>>> master', 1),
+    (b'# <<<<<<< HEAD', 0),
+    (b'# =======', 0),
+    (b'import my_module', 0),
+    (b'', 0),
+)
+
+
+@pytest.mark.parametrize(('input_s', 'expected_retval'), TESTS)
+def test_detect_merge_conflict(input_s, expected_retval, tmpdir):
+    path = os.path.join(tmpdir.strpath, 'file.txt')
+
+    with open(path, 'wb') as file_obj:
+        file_obj.write(input_s)
+
+    assert detect_merge_conflict([path]) == expected_retval