docker_compose_test returns 0 (success) even when dependent service fails to start

If we have service_a which depends on service_b being healthy, and service_b exits right away with a non-zero exit code, docker compose will bring down the services and report success (exit code 0). The reason being that service_a never reaches the "Started" state. So, --exit-code-from returns zero.

Here is a possible (untested) diff that might help fix the issue:

--- docker_compose_test.sh.orig
+++ docker_compose_test.sh
@@ -51,9 +51,21 @@
 echo "$docker_compose_up_cmd" | bash
 result=$?
 
-# Figure out the exit code of the test container incase it never actually started.
-EXIT_CODE=$(docker inspect $("${docker_compose_bin[@]}" -f $ABSOLUTE_COMPOSE_FILE_PATH ps -qa $DOCKER_COMPOSE_TEST_CONTAINER) --format='{{.State.ExitCode}}' 2>/dev/null)
-if [ "$EXIT_CODE" != "0" ] || [ -z "$EXIT_CODE" ]; then
-  echo "Error: $DOCKER_COMPOSE_TEST_CONTAINER container failed or never started!"
+# `docker compose up --exit-code-from` can still exit 0 in edge cases (e.g. the named service never
+# schedules while Compose treats the session as done). Resolve the service container via this compose
+# project and verify it actually exited successfully.
+SERVICE="$DOCKER_COMPOSE_TEST_CONTAINER"
+CID=$("${docker_compose_bin[@]}" -f "$ABSOLUTE_COMPOSE_FILE_PATH" ps -a -q "$SERVICE" 2>/dev/null | head -n 1) || CID=""
+
+EXIT_CODE="$( [ -n "$CID" ] && docker inspect "$CID" --format '{{.State.ExitCode}}' 2>/dev/null || echo "" )"
+STATUS="$( [ -n "$CID" ] && docker inspect "$CID" --format '{{.State.Status}}' 2>/dev/null || echo "not-found" )"
+
+# We must verify the container reached the 'exited' state. 
+# Containers in 'created' or 'running' state often have ExitCode 0, leading to false positives.
+if [ "$STATUS" = "exited" ] && [ "$EXIT_CODE" = "0" ]; then
+  echo "PASS ($SERVICE container exited with 0)"
+  exit 0
+fi
+
+echo "FAIL ($SERVICE status=$STATUS exit_code=${EXIT_CODE:-none} cid=${CID:-none})" >&2
 exit 1
-fi
-exit $result

Start in docker_compose_test.sh around the docker compose up command and the existing container inspection. Reproduce the dependent-service failure described in the issue, then verify that a test service which never reaches an exited state is reported as a failure rather than success, while a successfully exited service with code 0 still passes.