spring boot junit test runner

Junit5Runner.kt

@SpringBootApplication
class BitsApp

fun main(args: Array<String>) {
    val context = SpringApplicationBuilder().initializers(
            beans {
                bean {
                    Junit5Runner(listOf(
                            FirstTests::class.java,
                            VaultTests::class.java
                    ))
                }
            }
    ).sources(BitsApp::class.java).run(*args);

    System.exit(SpringApplication.exit(context))
}

class Junit5Runner(private val testClasses: List<Class<*>>) : ApplicationRunner, ExitCodeGenerator {
    private val log = LoggerFactory.getLogger(Junit5Runner::class.java)

    private var exitCode = 0

    override fun run(args: ApplicationArguments?) {
        val selectors = testClasses.map { DiscoverySelectors.selectClass(it) }.toTypedArray()
        val request = LauncherDiscoveryRequestBuilder.request()
                .selectors(*selectors)
                .build()

        val launcher = LauncherFactory.create()
        val testPlan = launcher.discover(request)

        logTests(launcher, request)

        val listener = SummaryGeneratingListener()
        val logListener = LoggingListener.forBiConsumer { t, u ->
            val msg = u.get()
            if (t == null) {
                log.info("test message=$msg")
            } else {
                log.error("test error message=$msg", t)
            }
        }
        launcher.registerTestExecutionListeners(listener, logListener)
        launcher.execute(request)

        val stream = ByteArrayOutputStream()
        val writer = PrintWriter(stream)

        if (listener.summary.totalFailureCount > 0) {
            listener.summary.printFailuresTo(writer)
            log.error("Junit Failures:$stream")
            exitCode = 2
        }

        listener.summary.printTo(writer)
        log.info("Junit Summary:$stream")
    }

    override fun getExitCode(): Int = exitCode

    // logs tests found for the request, optional
    private fun logTests(launcher: Launcher, request: LauncherDiscoveryRequest) {
        val testPlan = launcher.discover(request)

        testPlan.roots
                .flatMap { testPlan.getDescendants(it) }
                .filter { it.type == TestDescriptor.Type.TEST }
                .forEach {
                    log.info("uniqueId=${it.uniqueId} displayName=${it.displayName}")
                }
    }

}

When creating integration tests, JUnit5 works great; developers are familiar with its constructs (e.g., @Before) and its included assertions. Currently @SpringBootTest run well in the context of Maven or Gradle, so test classes can leverage Spring @Beans.

My goal is to continue using these tests as another application - outside of a build tool, and to package as a Spring uber jar. This simple Spring Boot app is my solution, which basically replicates JUnit5's ConsoleLauncher.

Implementation notes:

• Junit5Runner is not a @Component because this will cause Spring to recurse
• Tests classes must be put in src/main, NOT src/test. Otherwise, the Spring Boot plugin will not include them in the classpath of the bootJar (BOOT-INF/classes). Also:
• Must manually specify the test classes to Junit5Runner. Hence, they also cannot be in src/test. By explicitly naming the classes, they are loaded into the classpath and allows the JUnit5 Launcher to discover them.
  • I think this is also due to the packaging with the uber jar; e.g., I was able to get DiscoverySelectors.selectPackage working when run by ./gradlew bootRun, but no classes are found when run via java -jar
• To include the junit-engine, the dependency must be included as implementation rather than testImplementation

Resources:

• java -jar https://docs.oracle.com/en/java/javase/13/docs/specs/man/java.html
  • When you use -jar, the specified JAR file is the source of all user classes, and other class path settings are ignored.
• Spring Boot's nested jar https://docs.spring.io/spring-boot/docs/current/reference/html/appendix-executable-jar-format.html
• Usage https://github.com/chickenbane/rapidash-mvc
  • chickenbane/rapidash-mvc#4