Add test cases for pow that are meant to fail a type check

test_cases/stdlib/builtins/test_pow.py

@@ -71,3 +71,11 @@
 assert_type(pow(4.7, 9.2, None), Any)
 # See #7046 -- float for a positive 1st arg, complex otherwise
 assert_type((-95) ** 8.42, Any)
+
+# All of these should fail a type-checker
+# mypy will emit an error if any of them do not fail,
+# since we use --warn-unused-ignores when checking this subdirectory
+pow(1.9, 4, 6)  # type: ignore[misc]
+pow(complex(6), 6.2, 7)  # type: ignore[misc]
+pow(Fraction(), 5, 8)  # type: ignore[call-overload]
+Decimal("8.7") ** 3.14  # type: ignore[operator]

tests/mypy_test.py

@@ -14,6 +14,7 @@
 import argparse
 import os
 import re
+import shutil
 import subprocess
 import sys
 import tempfile
@@ -375,7 +376,11 @@ def test_the_test_cases(code: int, major: int, minor: int, args: argparse.Namesp
     if args.dry_run:
         this_code = 0
     else:
-        this_code = subprocess.run([sys.executable, "-m", "mypy", "test_cases", *flags]).returncode
+        # --warn-unused-ignores doesn't work for files inside typeshed.
+        # SO, to work around this, we copy the test_cases directory into a TemporaryDirectory.
+        with tempfile.TemporaryDirectory() as td:
+            shutil.copytree(Path("test_cases"), Path(td) / "test_cases")
+            this_code = subprocess.run([sys.executable, "-m", "mypy", td, *flags]).returncode
     code = max(code, this_code)
     return TestResults(code, num_test_case_files)