test(docker): probe repo-update by alias, with aborting guards

Author: qwO-Owp

.github/workflows/exp-opensuse.yml

@@ -1,5 +1,5 @@
 # Throwaway experiment (deleted after it runs): proves the fix in
-# docker/Dockerfile by forcing openSUSE-Tumbleweed-Update unreachable.
+# docker/Dockerfile by forcing the Update repo (alias repo-update) unreachable.
 # A dup --dry-run before the install forces the code path that failed:
 # "fixed" must build; "mutant" (the pre-fix Dockerfile) must fail.
 name: exp-opensuse
@@ -27,7 +27,7 @@ jobs:
           s = open(p).read()
           key = '\t\tzretry zypper --non-interactive --gpg-auto-import-keys refresh'
           assert s.count(key) == 1, 'anchor missing'
-          bad = ('\t\tzypper lr; f=$(grep -l "^\\[openSUSE-Tumbleweed-Update\\]" '
+          bad = ('\t\tzypper lr; f=$(grep -l "^\\[repo-update\\]" '
                  '/etc/zypp/repos.d/*.repo); test -n "$f"; '
                  'sed -i "s|^baseurl=.*|baseurl=http://invalid.invalid/|" $f; '
                  'grep baseurl $f; \\\n')
@@ -43,8 +43,17 @@ jobs:
             --build-arg BASE=opensuse/tumbleweed --build-arg CC=gcc \
             --build-arg BUILD_FLAGS='OPT=1 SAFE=1' . > build.log 2>&1
           rc=$?
-          grep -vE "Retrieving|^#[0-9]+ [0-9.]+ +[0-9]+ " build.log | tail -150
+          grep -v Retrieving build.log | tail -150
           echo "docker build rc=$rc for ${{ matrix.v }}"
-          # The sabotage itself must have run, or a failure proves nothing.
-          grep -qE "^#[0-9]+ [0-9.]+ baseurl=http://invalid.invalid/" build.log
-          if [ "${{ matrix.v }}" = fixed ]; then test "$rc" -eq 0; else test "$rc" -ne 0; fi
+          # Each guard aborts on its own (set +e is on): a failure for the
+          # wrong reason, or a pass that skipped the sabotage, proves nothing.
+          need() { grep -qE "$1" build.log || { echo "missing: $1"; exit 1; }; }
+          need "^#[0-9]+ [0-9.]+ baseurl=http://invalid.invalid/"
+          need "Failed to retrieve new repository metadata"
+          need "^#[0-9]+ [0-9.]+ \+ zypper --non-interactive dup --dry-run"
+          if [ "${{ matrix.v }}" = fixed ]; then
+            need "modifyrepo --disable repo-update"
+            test "$rc" -eq 0
+          else
+            test "$rc" -ne 0
+          fi