Add test case for new error based approach

Author: timothycrosley

isort/main.py

@@ -886,7 +886,7 @@ def main(argv: Optional[Sequence[str]] = None, stdin: Optional[TextIOWrapper] =
                     )
             print(f"Skipped {num_skipped} files")
 
-    if not config.quiet and (remapped_deprecated_args or deprecated_flags):  # pragma: no cover
+    if not config.quiet and (remapped_deprecated_args or deprecated_flags):
         if remapped_deprecated_args:
             warn(
                 "W0502: The following deprecated single dash CLI flags were used and translated: "

tests/test_main.py

@@ -231,6 +231,10 @@ def test_main(capsys, tmpdir):
     out, error = capsys.readouterr()
     assert "Skipped" in out
 
+    # warnings should be displayed if old flags are used
+    with pytest.warns(UserWarning):
+        main.main([str(python_file), "--recursive", "-fss"])
+    
 
 def test_isort_command():
     """Ensure ISortCommand got registered, otherwise setuptools error must have occured"""