fix: validate COMPOSE_FILE

See coop-cloud/organising#468.
See coop-cloud/organising#376.

tests/integration/app_deploy.bats

@@ -311,3 +311,20 @@ teardown(){
 
   _undeploy_app
 }
+
+# bats test_tags=slow
+@test "COMPOSE_FILE with \$COMPOSE_FILE override works" {
+  run sed -i 's/#COMPOSE_FILE="$COMPOSE_FILE:compose.extra_env.yml"/COMPOSE_FILE="$COMPOSE_FILE:compose.extra_env.yml"/g' \
+    "$ABRA_DIR/servers/$TEST_SERVER/$TEST_APP_DOMAIN.env"
+  assert_success
+
+  # NOTE(d1): --chaos used to bypass versions and access compose.extra_env.yml
+  run $ABRA app deploy "$TEST_APP_DOMAIN" \
+    --no-input --no-converge-checks --chaos
+  assert_success
+  assert_output --partial "compose.yml"
+  assert_output --partial "compose.extra_env.yml"
+
+  _undeploy_app
+  _reset_app
+}