diff --git a/.github/workflows/pytest.yml b/.github/workflows/pytest.yml
index c9939f8..02d87d9 100644
--- a/.github/workflows/pytest.yml
+++ b/.github/workflows/pytest.yml
@@ -3,7 +3,7 @@ name: CI_pytest_appendfilename
 # name    : pytest.yml
 # purpose : regularly run pytest on appendfilename
 # date    : [2024-10-31 Thu]
-# edit    : [2024-10-31 Thu]
+# edit    : [2024-11-12 Tue]
 
 on:
   push:
@@ -17,9 +17,17 @@ on:
     # - cron: "0 0 1 * *"  # once each 1st of a month, at 00:00 UTC (cf. https://crontab.guru/)
 
 jobs:
-  test-ubuntu-2404:
-    runs-on: ubuntu-24.04
-    timeout-minutes: 5
+  test:
+    strategy:
+      matrix:
+        # for a factorial test, an explicit selection of GitHUb runner images
+        # https://github.com/actions/runner-images?tab=readme-ov-file#available-images
+        # state of commit 23478d3 as visited on 2024-11-11 Mon
+        os: [ubuntu-20.04, ubuntu-22.04,ubuntu-24.04, windows-2019, windows-2022, macos-14]
+        python-version: ["3.10", "3.12"]
+    runs-on: ${{ matrix.os }}
+
+    timeout-minutes: 5  # Timeout for each job individually
 
     steps:
       - uses: actions/checkout@v4
@@ -28,52 +36,7 @@ jobs:
 
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.x'
-
-      - name: Install dependencies with PyPI
-        run: pip install -r requirements.txt
-
-      - name: run the check by pytest
-        run: |
-          python -m pytest -m "default"
-          python -m pytest -m "prepend"
-          python -m pytest -m "smart"
-
-  test-windows-2022:
-    runs-on: windows-2022
-    timeout-minutes: 5
-
-    steps:
-      - uses: actions/checkout@v4
-        # by [2024-10-23 Wed], this version possibly will be considered "old", cf.
-        # https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/
-
-      - uses: actions/setup-python@v5
-        with:
-          python-version: '3.x'
-
-      - name: Install dependencies with PyPI
-        run: pip install -r requirements.txt
-
-      - name: run the check by pytest
-        run: |
-          python -m pytest -m "default"
-          python -m pytest -m "prepend"
-          python -m pytest -m "smart"
-
-
-  test-macos-14:
-    runs-on: macos-14
-    timeout-minutes: 5
-
-    steps:
-      - uses: actions/checkout@v4
-        # by [2024-10-23 Wed], this version possibly will be considered "old", cf.
-        # https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/
-
-      - uses: actions/setup-python@v5
-        with:
-          python-version: '3.x'
+          python-version: ${{ matrix.python-version }}
 
       - name: Install dependencies with PyPI
         run: pip install -r requirements.txt
diff --git a/pytest.ini b/pytest.ini
index 8f466c6..1bd280b 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -1,5 +1,5 @@
 [pytest]
-Markers =
+markers =
     default:  appendfilename's default string insertions
     prepend:  appendfilename's optional -p/--prepend flag
     smart:    appendfilename's optional --smart-prepend flag
diff --git a/test_appendfilename.py b/test_appendfilename.py
index e930c07..a680818 100755
--- a/test_appendfilename.py
+++ b/test_appendfilename.py
@@ -283,7 +283,7 @@ def test_smart_prepend(arg1, arg2, arg3):
         old_filename_no_timestamp = old_filename[8:]
 
     # pattern `--short`  # currently fails
-    elif re.search(r"^\d{4}[012]\d[012]\d", old_filename):
+    elif re.search(r"^\d{4}[012]\d[0-3]\d", old_filename):
         time_stamp = old_filename[:6]
         time_stamp_separator = old_filename[6]
         old_filename_no_timestamp = old_filename[7:]
diff --git a/test_generator.org b/test_generator.org
index 282aac6..fe27ac8 100755
--- a/test_generator.org
+++ b/test_generator.org
@@ -140,7 +140,7 @@ pytest-3 test_appendfilename.py -m "default and prepend" -v
 
    #+begin_src shell :tangle pytest.ini
 [pytest]
-Markers =
+markers =
     default:  appendfilename's default string insertions
     prepend:  appendfilename's optional -p/--prepend flag
     smart:    appendfilename's optional --smart-prepend flag
@@ -467,7 +467,7 @@ def test_smart_prepend(arg1, arg2, arg3):
         old_filename_no_timestamp = old_filename[8:]
 
     # pattern `--short`  # currently fails
-    elif re.search(r"^\d{4}[012]\d[012]\d", old_filename):
+    elif re.search(r"^\d{4}[012]\d[0-3]\d", old_filename):
         time_stamp = old_filename[:6]
         time_stamp_separator = old_filename[6]
         old_filename_no_timestamp = old_filename[7:]