github: add ability to "unskip" skipped tests

Author: maykathm

.github/workflows/spread-results-reporter.yaml

@@ -162,6 +162,7 @@ jobs:
 
           if find . -name skipped_tests_list.txt | grep -q .; then
             echo "## Skipped tests from [snapd-testing-skip](https://github.com/canonical/snapd-testing-skip)" >> report
+            echo "*If you wish to have any of the below tests run in your PR, in your PR description, add 'unskip:' followed by a copy-and-pasted list of the below tests you wish to run*" >> report
             find . -name skipped_tests_list.txt -exec cat {} \; | tr ' ' '\n' | grep . | sort -u | awk '{print "- "$1}' >> report
           fi
 

.github/workflows/spread-tests.yaml

@@ -240,6 +240,30 @@ jobs:
               printf "" > "$RUN_TESTS_FILE"
           fi
 
+    - name: Check un-skip tests in PR description
+      if: ${{ github.event.pull_request.number != "" }}
+      run: |
+          body="$(gh pr view ${{ github.event.pull_request.number }} --json body --jq .body)"
+
+          # Grab "unskip:" and the following lines that start with "-".
+          unskip_yaml="$(
+              grep -ozP '(?ms)^[[:space:]]*unskip:[[:space:]]*\n(?:[[:space:]]*-[^\n]*\n?)*' <<<"$body" |
+                  tr '\0' '\n' || true
+          )"
+          if [ -z "$unskip_yaml" ]; then
+              exit 0
+          fi
+
+          mapfile -t unskip_tests < <(printf '%s\n' "$unskip_yaml" | yq -r '.unskip[]')
+          UNSKIP_TESTS="${unskip_tests[*]}"
+
+          if [ -z "$UNSKIP_TESTS" ]; then
+              exit 0
+          fi
+
+          echo "UNSKIP_TESTS=$UNSKIP_TESTS" >> "$GITHUB_ENV"
+          
+
     - name: Checkout snapd-testing-skip
       if: ${{ env.SKIP_SPREAD_LABEL != 'true' && env.RUN_TESTS == 'true' }}
       uses: actions/checkout@v6
@@ -273,6 +297,13 @@ jobs:
               backend=$(yq -r '."spread-backend" // ".*"' "$file")
               if [[ "$expire" > "$today" ]] && grep -Eq "$system" <<<"${{ inputs.systems }}" && grep -Eq "^$backend$" <<<"$SPREAD_BACKEND"; then
                   task=$(yq -r '."spread-task"' "$file")
+                  for unskip_test in ${UNSKIP_TESTS:-}; do
+                      if [[ "$unskip_test" == "$backend:$system:$task" ]]; then
+                          echo "Ignoring skip rule for $backend:$system:$task due to unskip entry"
+                          continue 2
+                      fi
+                  done
+
                   SNAPD_TESTS_SKIP="${SNAPD_TESTS_SKIP} $(echo "$spread_list" | tr ' ' '\n' | grep "$task$" | tr '\n' ' ')"
                   spread_list=$(echo "$spread_list" | tr ' ' '\n' | grep -vE "$task$" | tr '\n' ' ')
                   echo "$spread_list" > "$RUN_TESTS_FILE"