Start initial flow for downgrade tests

.github/workflows/test-packages-action-macos.yml

@@ -238,7 +238,7 @@ jobs:
           SKIP_INITIAL_GH_ACTIONS_FAILURES: "1"
         run: |
           sudo -E nox --force-color -e ${{ inputs.nox-session }} -- ${{ matrix.test-chunk }} \
-          ${{ contains(matrix.test-chunk, 'upgrade') && format('--prev-version {0}', matrix.version) || ''}}
+          ${{ matrix.version && format('--prev-version {0}', matrix.version) || ''}}
 
       - name: Run Package Tests
         env:
@@ -252,7 +252,7 @@ jobs:
           COVERAGE_CONTEXT: ${{ inputs.distro-slug }}
         run: |
           sudo -E nox --force-color -e ${{ inputs.nox-session }} -- ${{ matrix.test-chunk }} \
-          ${{ contains(matrix.test-chunk, 'upgrade') && format('--prev-version {0}', matrix.version) || ''}}
+          ${{ matrix.version && format('--prev-version {0}', matrix.version) || ''}}
 
       - name: Fix file ownership
         run: |

.github/workflows/test-packages-action.yml

@@ -268,13 +268,13 @@ jobs:
         run: |
           tools --timestamps --timeout-secs=1800 vm testplan --skip-requirements-install \
             --nox-session=${{ inputs.nox-session }} ${{ inputs.distro-slug }} -- ${{ matrix.test-chunk }} \
-            ${{ contains(matrix.test-chunk, 'upgrade') && format('--prev-version {0}', matrix.version) || ''}}
+            ${{ matrix.version && format('--prev-version {0}', matrix.version) || ''}}
 
       - name: Run Package Tests
         run: |
           tools --timestamps --no-output-timeout-secs=1800 --timeout-secs=14400 vm test --skip-requirements-install \
           --nox-session=${{ inputs.nox-session }} --rerun-failures ${{ inputs.distro-slug }} -- ${{ matrix.test-chunk }} \
-          ${{ contains(matrix.test-chunk, 'upgrade') && format('--prev-version {0}', matrix.version) || ''}}
+          ${{ matrix.version && format('--prev-version {0}', matrix.version) || ''}}
 
       - name: Download Test Run Artifacts
         id: download-artifacts-from-vm

noxfile.py

@@ -1797,6 +1797,16 @@ def test_pkgs_onedir(session):
             "--no-uninstall",
             "pkg/tests/upgrade/",
         ],
+        "downgrade": [
+            "--downgrade",
+            "--no-uninstall",
+            "pkg/tests/downgrade/",
+        ],
+        "downgrade-classic": [
+            "--downgrade",
+            "--no-uninstall",
+            "pkg/tests/downgrade/",
+        ],
         "download-pkgs": [
             "--download-pkgs",
             "pkg/tests/download/",

tools/ci.py

@@ -715,6 +715,7 @@ def pkg_matrix(
         # we allow for 3006.0 jobs to run, because then
         # we will have arm64 onedir packages to upgrade from
         sessions.append("upgrade")
+        sessions.append("downgrade")
     # TODO: Remove this block when we reach version 3009.0, we will no longer be testing upgrades from classic packages
     if (
         distro_slug
@@ -729,12 +730,13 @@ def pkg_matrix(
     ):
         # Packages for these OSs where never built for classic previously
         sessions.append("upgrade-classic")
+        sessions.append("downgrade-classic")
 
     for session in sessions:
         versions: list[str | None] = [None]
-        if session == "upgrade":
+        if session in ("upgrade", "downgrade"):
             versions = [str(version) for version in testing_releases]
-        elif session == "upgrade-classic":
+        elif session in ("upgrade-classic", "downgrade-classic"):
             versions = [
                 str(version)
                 for version in testing_releases