Fix check-merge-conflict against binary files

tests/check_merge_conflict_test.py

@@ -3,12 +3,14 @@ from __future__ import unicode_literals
 
 import io
 import os
+import shutil
 
 import pytest
 
 from pre_commit_hooks.check_merge_conflict import detect_merge_conflict
 from pre_commit_hooks.util import cmd_output
 from testing.util import cwd
+from testing.util import get_resource_path
 from testing.util import write_file
 
 
@@ -109,6 +111,12 @@ def test_merge_conflicts_ok(ok_contents):
     assert detect_merge_conflict(['f1']) == 0
 
 
+@pytest.mark.usefixtures('f1_is_a_conflict_file')
+def test_ignores_binary_files():
+    shutil.copy(get_resource_path('img1.jpg'), 'f1')
+    assert detect_merge_conflict(['f1']) == 0
+
+
 @pytest.mark.usefixtures('in_tmpdir')
 def test_does_not_care_when_not_in_a_merge():
     with io.open('README.md', 'w') as readme_file: