improve integration tests

tests/integration/test_plugins.py

@@ -1,5 +1,6 @@
 """Integration tests for plugin loading."""
 from flake8.main import application
+from flake8.main.cli import main
 
 LOCAL_PLUGIN_CONFIG = "tests/fixtures/config_files/local-plugin.ini"
 LOCAL_PLUGIN_PATH_CONFIG = "tests/fixtures/config_files/local-plugin-path.ini"
@@ -65,3 +66,32 @@ def test_enable_local_plugin_at_non_installed_path():
 
     assert app.check_plugins is not None
     assert app.check_plugins["XE"].plugin.name == "ExtensionTestPlugin2"
+
+
+class AlwaysErrors:
+    name = "AlwaysError"
+    version = "1"
+
+    def __init__(self, tree):
+        pass
+
+    def run(self):
+        yield 1, 0, "ABC123 error", type(self)
+
+
+def test_plugin_gets_enabled_by_default(tmp_path, capsys):
+    cfg_s = f"""\
+[flake8:local-plugins]
+extension =
+    ABC = {AlwaysErrors.__module__}:{AlwaysErrors.__name__}
+"""
+    cfg = tmp_path.joinpath("tox.ini")
+    cfg.write_text(cfg_s)
+
+    t_py = tmp_path.joinpath("t.py")
+    t_py.touch()
+
+    assert main((str(t_py), "--config", str(cfg))) == 1
+    out, err = capsys.readouterr()
+    assert out == f"{t_py}:1:1: ABC123 error\n"
+    assert err == ""