(Should fix) oppia#3789: Fix flaky test retry mechanism for Bazel CI (o…

…ppia#3908)

* Update unit_tests.yml

* Break test to demonstrate retry in CI.

* Introduce build failure.

* Undo break.

.github/workflows/unit_tests.yml

@@ -235,10 +235,19 @@ jobs:
  # Attempt to build 5 times in case there are flaky builds.
  # TODO(#3759): Remove this once there are no longer app test build failures.
  i=0
+ # Disable exit-on-first-failure.
+ set +e
  while [ $i -ne 5 ]; do
  i=$(( $i+1 ))
+ echo "Attempt $i/5 to build test targets"
  bazel build --keep_going --remote_http_cache=$BAZEL_REMOTE_CACHE_URL --google_credentials=./config/oppia-dev-workflow-remote-cache-credentials.json -- $BAZEL_TEST_TARGETS
  done
+ # Capture the error code of the final command run (which should be a success if there isn't a real build failure).
+ last_error_code=$?
+ # Reenable exit-on-first-failure.
+ set -e
+ # Exit only if the most recent exit was a failure (by using a subshell).
+ (exit $last_error_code)
 
  - name: Build Oppia Tests (without caching, or on a fork)
  if: ${{ env.ENABLE_CACHING == 'false' || ((github.ref != 'refs/heads/develop' || github.event_name != 'push') && (github.event.pull_request.head.repo.full_name != 'oppia/oppia-android')) }}
@@ -248,10 +257,19 @@ jobs:
  # Attempt to build 5 times in case there are flaky builds.
  # TODO(#3759): Remove this once there are no longer app test build failures.
  i=0
+ # Disable exit-on-first-failure.
+ set +e
  while [ $i -ne 5 ]; do
  i=$(( $i+1 ))
+ echo "Attempt $i/5 to build test targets"
  bazel build --keep_going -- $BAZEL_TEST_TARGETS
  done
+ # Capture the error code of the final command run (which should be a success if there isn't a real build failure).
+ last_error_code=$?
+ # Reenable exit-on-first-failure.
+ set -e
+ # Exit only if the most recent exit was a failure (by using a subshell).
+ (exit $last_error_code)
  - name: Run Oppia Tests (with caching, non-fork only)
  if: ${{ env.ENABLE_CACHING == 'true' && ((github.ref == 'refs/heads/develop' && github.event_name == 'push') || (github.event.pull_request.head.repo.full_name == 'oppia/oppia-android')) }}
  env: