test: cover whitespace-only slugify input

Test whitespace-only slugify returns empty (issue #169)

Author: ltsyk

test.py

@@ -655,3 +655,9 @@ def test_multivalued_options_with_text(self):
 
 if __name__ == '__main__':  # pragma: nocover
     unittest.main()
+
+
+def test_slugify_whitespace_only_returns_empty():
+    from slugify import slugify
+    assert slugify("   ") == ""
+    assert slugify("\t\n") == ""