add hook to the pytest vscode plugin to determine how many xdist work…

…ers to use based on how many tests are selected

python_files/vscode_pytest/__init__.py

@@ -16,7 +16,7 @@
 sys.path.append(os.fspath(script_dir / "lib" / "python"))
 
 from testing_tools import socket_manager  # noqa: E402
-from typing import Any, Dict, List, Optional, Union, TypedDict, Literal  # noqa: E402
+from typing import Any, Dict, Generator, List, Optional, Union, TypedDict, Literal  # noqa: E402
 
 
 class TestData(TypedDict):
@@ -881,3 +881,12 @@ def send_post_request(
             f"Plugin error, exception thrown while attempting to send data[vscode-pytest]: {error} \n[vscode-pytest] data: \n{data}\n",
             file=sys.stderr,
         )
+
+
+@pytest.hookimpl(hookwrapper=True)
+def pytest_xdist_auto_num_workers(config: pytest.Config) -> Generator[None, int, int]:
+    """determine how many workers to use based on how many tests were selected in the test explorer"""
+    num_workers = (yield).get_result()
+    if "vscode_pytest" in config.option.plugins:
+        return min(num_workers, len(config.option.file_or_dir))
+    return num_workers