Improve test so we are sure the exclude section has this side-effect

Author: maerteijn

test/test_plugin.py

@@ -330,12 +330,15 @@ def foo():
     assert diag["code"] == "unreachable"
 
 
-def test_exclude_path_match_mypy_not_run(tmpdir, workspace):
+def test_config_exclude(tmpdir, workspace):
     """When exclude is set in config then mypy should not run for that file."""
     doc = Document(DOC_URI, workspace, DOC_TYPE_ERR)
 
     plugin.pylsp_settings(workspace._config)
-    workspace.update_config({"pylsp": {"plugins": {"pylsp_mypy": {"exclude": [doc.path]}}}})
+    workspace.update_config({"pylsp": {"plugins": {"pylsp_mypy": {}}}})
     diags = plugin.pylsp_lint(workspace._config, workspace, doc, is_saved=False)
+    assert diags[0]["message"] == TYPE_ERR_MSG
 
-    assert not diags
+    workspace.update_config({"pylsp": {"plugins": {"pylsp_mypy": {"exclude": [doc.path]}}}})
+    diags = plugin.pylsp_lint(workspace._config, workspace, doc, is_saved=False)
+    assert diags == []