Tests should fail if mypy fails to find the stubs that are to be tested.
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,7 +1,7 @@
 [mypy]
 check_untyped_defs = True
 ignore_errors = False
-ignore_missing_imports = True
+ignore_missing_imports = False
 strict_optional = True
 no_error_summary = True
 no_color_output = True