Handle pre-release pytest CI setup

Author: Copilot

.github/workflows/pr-check.yml

@@ -172,6 +172,19 @@ jobs:
         with:
           python-version: ${{ matrix.python }}
 
+      - name: Install base Python requirements
+        uses: brettcannon/pip-secure-install@92f400e3191171c1858cc0e0d9ac6320173fdb0c # v1.0.0
+        with:
+          requirements-file: '"${{ env.special-working-directory-relative }}/requirements.txt"'
+          options: '-t "${{ env.special-working-directory-relative }}/python_files/lib/python" --no-cache-dir --implementation py'
+
+      - name: Install test requirements
+        run: python -m pip install --upgrade -r build/test-requirements.txt
+
+      - name: Remove pytest-black for pre-release pytest
+        if: matrix.pytest-version == 'pytest@pre-release'
+        run: python -m pip uninstall -y pytest-black
+
       - name: Install specific pytest version
         if: matrix.pytest-version == 'pytest@pre-release'
         run: |
@@ -184,14 +197,6 @@ jobs:
 
       - name: Install specific pytest version
         run: python -m pytest --version
-      - name: Install base Python requirements
-        uses: brettcannon/pip-secure-install@92f400e3191171c1858cc0e0d9ac6320173fdb0c # v1.0.0
-        with:
-          requirements-file: '"${{ env.special-working-directory-relative }}/requirements.txt"'
-          options: '-t "${{ env.special-working-directory-relative }}/python_files/lib/python" --no-cache-dir --implementation py'
-
-      - name: Install test requirements
-        run: python -m pip install --upgrade -r build/test-requirements.txt
 
       - name: Run Python unit tests
         run: python python_files/tests/run_all.py

python_files/tests/pytestadapter/test_discovery.py

@@ -1,5 +1,6 @@
 # Copyright (c) Microsoft Corporation. All rights reserved.
 # Licensed under the MIT License.
+import importlib.util
 import json
 import os
 import pathlib
@@ -13,6 +14,8 @@
 
 from . import expected_discovery_test_output, helpers
 
+PYTEST_BLACK_AVAILABLE = importlib.util.find_spec("pytest_black") is not None
+
 
 def test_compact_discovery_payload_keeps_absolute_tree_until_return(tmp_path, monkeypatch):
     monkeypatch.setattr(vscode_pytest, "ERRORS", [])
@@ -476,10 +479,14 @@ def test_config_sub_folder():
             expected_discovery_test_output.ruff_test_expected_output,
             "--ruff",
         ),
-        (
+        pytest.param(
             "2496-black-formatter",
             expected_discovery_test_output.black_formatter_expected_output,
             "--black",
+            marks=pytest.mark.skipif(
+                not PYTEST_BLACK_AVAILABLE,
+                reason="pytest-black is not installed for this pytest environment",
+            ),
         ),
     ],
 )