test: add test for #17 (#18)

tests/checkers/test_base.py

@@ -0,0 +1,12 @@
+from textwrap import dedent
+
+
+def test_checker_unknown_call(helpers):
+    """
+    When the function call is not recognized, no error is raised from `Checker`.
+    """
+    sample_code = """
+        class Model():
+            _normalize_title = whatever()()
+    """
+    assert helpers.results(dedent(sample_code)) == set()