Enforce DOCKER_IMAGE is set - fail early if missing

- Add validation in workflow to check DOCKER_IMAGE is set before running tests
- Update TestMain to fail immediately if DOCKER_IMAGE is empty instead of defaulting to mysql:8.0
- Add validation for TIDB_VERSION as well
- This prevents silent failures and ensures correct Docker images are used

Author: zph

.github/workflows/main.yml

@@ -190,9 +190,18 @@ jobs:
           export PATH="${{ github.workspace }}/bin:$PATH"
           if [ "${{ matrix.db_type }}" == "tidb" ]; then
             export TIDB_VERSION=${{ matrix.db_version }}
+            if [ -z "$TIDB_VERSION" ]; then
+              echo "ERROR: TIDB_VERSION is not set for TiDB test"
+              exit 1
+            fi
             go test -tags=testcontainers -v ./mysql/... -run WithTestcontainers -timeout=30m
           else
             export DOCKER_IMAGE=${{ matrix.docker_image }}
+            if [ -z "$DOCKER_IMAGE" ]; then
+              echo "ERROR: DOCKER_IMAGE is not set for ${{ matrix.db_type }} test"
+              exit 1
+            fi
+            echo "Using Docker image: $DOCKER_IMAGE"
             go test -tags=testcontainers -v ./mysql/... -run WithTestcontainers -timeout=30m
           fi
   release:

mysql/testcontainers_testmain.go

@@ -42,10 +42,12 @@ func TestMain(m *testing.M) {
 		os.Exit(code)
 	}
 
-	// Default to MySQL 8.0, but allow override via DOCKER_IMAGE env var
+	// Require DOCKER_IMAGE to be set - fail early if missing
 	mysqlImage := os.Getenv("DOCKER_IMAGE")
 	if mysqlImage == "" {
-		mysqlImage = "mysql:8.0"
+		os.Stderr.WriteString("ERROR: DOCKER_IMAGE environment variable is not set. This is required for MySQL/Percona/MariaDB tests.\n")
+		os.Stderr.WriteString("Please set DOCKER_IMAGE to the appropriate Docker image (e.g., mysql:5.6, percona:8.0, mariadb:10.10)\n")
+		os.Exit(1)
 	}
 
 	// Start shared container before running tests