Add test for existing preferred-modules functionality (#8093)

Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/checkers/unittest_imports.py b/tests/checkers/unittest_imports.py
index 8be4d63ff..ed5c13805 100644
--- a/tests/checkers/unittest_imports.py
+++ b/tests/checkers/unittest_imports.py
@@ -114,3 +114,26 @@ class TestImportsChecker(CheckerTestCase):
         )
         with self.assertAddsMessages(msg):
             self.checker.visit_importfrom(import_from)
+
+    @staticmethod
+    def test_preferred_module(capsys: CaptureFixture[str]) -> None:
+        """
+        Tests preferred-module configuration option
+        """
+        # test preferred-modules case with base module import
+        Run(
+            [
+                f"{os.path.join(REGR_DATA, 'preferred_module')}",
+                "-d all",
+                "-e preferred-module",
+                # prefer sys instead of os (for triggering test)
+                "--preferred-modules=os:sys",
+            ],
+            exit=False,
+        )
+        output, errors = capsys.readouterr()
+
+        # assert that we saw preferred-modules triggered
+        assert "Prefer importing 'sys' instead of 'os'" in output
+        # assert there were no errors
+        assert len(errors) == 0