ci: towards testing non-LTS ubuntu versions

.github/workflows/unit-test.yaml

@@ -26,7 +26,16 @@ on:
 jobs:
   unit-tests:
     name: ${{ matrix.name }}
-    runs-on: ubuntu-${{ matrix.ubuntu_version }}
+
+    # runs-on can only be configured to the LTS releases of ubuntu (18.04,
+    # 20.04, ...), so if we want to test against the latest non-LTS release, we
+    # must compromise when configuring runs-on and configure runs-on to be the
+    # latest LTS release instead.
+    #
+    # This can have consequences because actions like actions/setup-python will
+    # mount cached installations associated with the chosen runs-on environment.
+    #
+    runs-on: ${{ format('ubuntu-{0}', matrix.runs_on || matrix.ubuntu_version) }}
     container: ubuntu:${{ matrix.ubuntu_version }}
 
     strategy:
@@ -34,11 +43,11 @@ jobs:
       matrix:
         include:
           - name: "Unit tests: Ubuntu 18.04, Py 3.6"
-            ubuntu_version: 18.04
-            python_version: 3.6
+            ubuntu_version: "18.04"
+            python_version: "3.6"
           - name: "Unit tests: Ubuntu 20.04, Py 3.9"
-            ubuntu_version: 20.04
-            python_version: 3.9
+            ubuntu_version: "20.04"
+            python_version: "3.9"
 
     steps:
       - uses: actions/checkout@v2
@@ -47,16 +56,31 @@ jobs:
           python-version: ${{ matrix.python_version }}
 
       - name: Install venv, git and setup venv
+        timeout-minutes: 2
         run: |
-          apt-get update --yes && apt-get install --yes python3-venv git
+          export DEBIAN_FRONTEND=noninteractive
+          apt-get update
+          apt-get install --yes \
+              python3-venv \
+              git
+
           python3 -m venv /srv/venv
           echo '/srv/venv/bin' >> $GITHUB_PATH
 
-      - name: Cache pip deps
+      # WARNING: This action loads a cache of pip dependencies based on the
+      #          declared key, and it will save a cache for that key on job
+      #          completion. Make sure to update the key to bust the cache
+      #          properly if you make a change that should influence it.
+      - name: Load cached Python dependencies
         uses: actions/cache@v2
         with:
           path: /srv/venv/
-          key: pip-${{ matrix.ubuntu_version }}-${{ matrix.python_version }}-${{ hashFiles('*setup.py', '*dev-requirements.txt') }}
+          key: >-
+            pip-
+            ${{ matrix.runs_on }}-
+            ${{ matrix.ubuntu_version }}-
+            ${{ matrix.python_version }}-
+            ${{ hashFiles('setup.py', 'dev-requirements.txt', '.github/workflows/unit-test.yaml') }}
 
       - name: Install Python dependencies
         run: |
@@ -66,9 +90,7 @@ jobs:
           pip freeze
 
       - name: Run unit tests
-        run: |
-          pytest --verbose --maxfail=2 --color=yes --cov=tljh tests/
+        run: pytest --verbose --maxfail=2 --color=yes --cov=tljh tests/
 
       - name: Upload code coverage stats
-        run: |
-          codecov
+        run: codecov