Honor selected standard-library files in the test runner

tests/README.md

@@ -145,6 +145,8 @@ Run using
 This test compares the stdlib stubs against the objects at runtime. Because of
 this, the output depends on which version of Python and on what kind of system
 it is run.
+To check specific modules instead of the entire standard library, pass their
+import names, for example `python tests/stubtest_stdlib.py getopt`.
 As such, if you run this test locally, it may complain about system-specific
 differences (in e.g., `socket`) that the type system cannot capture or our stubtest settings
 in CI do not account for. If you run into this issue, consider opening a draft PR and letting CI

tests/runtests.py

@@ -92,7 +92,8 @@ def main() -> None:
     stubtest_result: subprocess.CompletedProcess[bytes] | None = None
 
     print("\nRunning pre-commit...")
-    pre_commit_result = subprocess.run(["pre-commit", "run", "--files", *path.rglob("*")], check=False)
+    files = [path] if path.is_file() else list(path.rglob("*"))
+    pre_commit_result = subprocess.run(["pre-commit", "run", "--files", *files], check=False)
 
     print("\nRunning check_typeshed_structure.py...")
     check_structure_result = subprocess.run([sys.executable, "tests/check_typeshed_structure.py"], check=False)
@@ -154,7 +155,7 @@ def main() -> None:
     if mypy_result.returncode == 0:
         if folder == "stdlib":
             print("\nRunning stubtest...")
-            stubtest_result = subprocess.run([sys.executable, "tests/stubtest_stdlib.py", stub], check=False)
+            stubtest_result = subprocess.run([sys.executable, "tests/stubtest_stdlib.py", Path(stub).stem], check=False)
         else:
             if run_stubtest:
                 print("\nRunning stubtest...")

tests/stubtest_stdlib.py

@@ -11,13 +11,14 @@
 
 import subprocess
 import sys
+from collections.abc import Sequence
 from pathlib import Path
 
 from ts_utils.paths import TS_BASE_PATH, allowlists_path
 from ts_utils.utils import allowlist_stubtest_arguments
 
 
-def run_stubtest(typeshed_dir: Path) -> int:
+def run_stubtest(typeshed_dir: Path, modules: Sequence[str] = ()) -> int:
     # Note when stubtest imports distutils, it will likely actually import setuptools._distutils
     # This is fine because we don't care about distutils and allowlist all errors from it
     # https://github.com/python/typeshed/pull/10253#discussion_r1216712404
@@ -26,13 +27,16 @@ def run_stubtest(typeshed_dir: Path) -> int:
         sys.executable,
         "-m",
         "mypy.stubtest",
-        "--check-typeshed",
+        *(modules if modules else ["--check-typeshed"]),
         "--show-traceback",
         "--strict-type-check-only",
         "--custom-typeshed-dir",
         str(typeshed_dir),
         *allowlist_stubtest_arguments("stdlib"),
     ]
+    if modules:
+        # Entries for modules outside this selection are expected to be unused.
+        cmd.append("--ignore-unused-allowlist")
     print(" ".join(cmd), file=sys.stderr)
     try:
         subprocess.run(cmd, check=True)
@@ -56,4 +60,4 @@ def run_stubtest(typeshed_dir: Path) -> int:
 
 
 if __name__ == "__main__":
-    sys.exit(run_stubtest(typeshed_dir=TS_BASE_PATH))
+    sys.exit(run_stubtest(typeshed_dir=TS_BASE_PATH, modules=sys.argv[1:]))