Specify the config file when doing a self check (!) (#5279)

Fortunately only one error crept in while we weren't doing that.

Author: msullivan

mypy/test/helpers.py

@@ -39,11 +39,6 @@ def run_mypy(args: List[str]) -> None:
         pytest.fail(msg="Sample check failed", pytrace=False)
 
 
-def use_builtins_fixtures(options):
-    root_dir = dirname(dirname(dirname(__file__)))
-    options.path_prefix = os.path.join(root_dir, 'test-data', 'unit', 'lib-stub')
-
-
 def assert_string_arrays_equal(expected: List[str], actual: List[str],
                                msg: str) -> None:
     """Assert that two string arrays are equal.

mypy/test/testselfcheck.py

@@ -5,7 +5,8 @@
 
 class SelfCheckSuite(Suite):
     def test_mypy_package(self) -> None:
-        run_mypy(['-p', 'mypy'])
+        run_mypy(['--config-file', 'mypy_self_check.ini', '-p', 'mypy'])
 
     def test_testrunner(self) -> None:
-        run_mypy(['runtests.py', 'waiter.py'])
+        run_mypy(['--config-file', 'mypy_self_check.ini',
+                  '--no-warn-unused-configs', 'runtests.py', 'waiter.py'])