ci(test): enforce coverage-based test selection on PRs

Flip the shadow --only-changes selection to --select-enforce on PR runs for the github (GNU/intel) jobs and the self-hosted Phoenix/Frontier jobs. PRs now run only the tests whose recorded coverage overlaps the changed files; the conservative ladder in coverage.py falls back to run-all for non-.fpp changes and .fpp files no test covers. Backstops retained: the NVHPC jobs still run --test-all on every PR (pre-merge full check), and pushes to master run the full suite (SELECT empty).

Author: sbryngelson

.github/workflows/common/test.sh

@@ -57,12 +57,14 @@ if [ -n "${job_shard:-}" ]; then
     shard_opts="--shard $job_shard"
 fi
 
-# Coverage-based test selection in SHADOW mode on PRs: prints what it WOULD select but the
-# full suite still runs (no --select-enforce). Changed files come from git detection
-# (self-healing deepen) since the SLURM job doesn't receive the paths-filter list.
+# Coverage-based test selection ENFORCED on PRs: runs only tests whose recorded coverage
+# overlaps the PR's changed files (conservative ladder; non-.fpp and uncovered-.fpp changes
+# fall back to run-all). Pushes to master run the full suite as a backstop. Changed files
+# come from git detection (self-healing deepen) since the SLURM job doesn't receive the
+# paths-filter list.
 select_opts=""
 if [ "${GITHUB_EVENT_NAME:-}" = "pull_request" ]; then
-    select_opts="--only-changes"
+    select_opts="--only-changes --select-enforce"
 fi
 
 ./mfc.sh test -v --max-attempts 3 --no-build $select_opts -a -j $n_test_threads $rdma_opts $device_opts $build_opts $shard_opts -- -c $job_cluster

.github/workflows/test.yml

@@ -264,11 +264,13 @@ jobs:
       - name: Test
         if:   '!matrix.nvhpc'
         run:  |
-          # Coverage-based test selection in SHADOW mode on PRs: the selector
-          # prints what it WOULD run, but the full suite still runs (no
-          # --select-enforce). Enforcement is a separate, later change.
+          # Coverage-based test selection ENFORCED on PRs: runs only the tests whose
+          # recorded coverage overlaps the PR's changed files (conservative ladder in
+          # coverage.py — non-.fpp changes and .fpp files no test covers fall back to
+          # run-all). Pushes to master run the full suite (SELECT empty) as a backstop,
+          # and the NVHPC jobs below still run --test-all as a pre-merge full check.
           SELECT=()
-          [ "${{ github.event_name }}" = "pull_request" ] && SELECT=(--only-changes --changed-files "$CHANGED_FILES")
+          [ "${{ github.event_name }}" = "pull_request" ] && SELECT=(--only-changes --select-enforce --changed-files "$CHANGED_FILES")
           /bin/bash mfc.sh test -v --max-attempts 3 -j $(nproc) "${SELECT[@]}" $TEST_ALL $TEST_PCT $PRECISION
         env:
           TEST_ALL: ${{ matrix.mpi == 'mpi' && '--test-all' || '' }}