Add new hook

tests/detect_datetime_now_test.py

@@ -0,0 +1,17 @@
+import pytest
+
+from pre_commit_hooks.detect_datetime_now import main
+
+TESTS = (
+    ('from datetime import datetime\ncurrent_date = datetime.now()', 1),
+    ('from datetime import datetime', 0),
+)
+
+
+@pytest.mark.parametrize(('input_s', 'expected_return_value'), TESTS)
+def test_datetime_now_usage(input_s, expected_return_value, tmpdir):
+    """Test behavior with no datetime.now being used on code."""
+    path = tmpdir.join('test_script.py')
+    path.write(input_s)
+    using_datetime = main([path.strpath])
+    assert using_datetime == expected_return_value