Provide dependency management for Awaitility

[dsyer]

A common use case for @ExtendWith(OutputCaptureExtension.class) is to wait for some text to appear in logs, signifying that something happened in the app under test, but not accessible to direct monitoring via an API. It would be useful to have methods or utilities that directly knew about how to do this as quickly as possible, e.g.

	@Test
	public void contextLoads(CapturedOutput output) throws Exception {
		output.waitFor("bar", Duration.ofSeconds(10));
		assertThat(output.getErr()).doesNotContain("foo");
	}

[dsyer]

I guess a utility (e.g. in Spring Framework) would work - turning the example above into a method call:

	@Test
	public void contextLoads(CapturedOutput output) throws Exception {
		Timeouts.waitFor(() -> assertThat(output.getErr()).contains("bar")), Duration.ofSeconds(10));
		assertThat(output.getErr()).doesNotContain("foo");
	}

Cf Guava TimeLimiter for similar features.

[dsyer]

Found something in JUnit:

	@Test
	public void contextLoads(CapturedOutput output) throws Exception {
		assertTimeout(Duration.ofSeconds(10), () -> assertThat(output.getErr()).contains("bar")));
		assertThat(output.getErr()).doesNotContain("foo");
	}

but it doesn't do what I want because it only executes the supplier once. I need it to loop and try again.

[dsyer]

Here's one that works:

	private RetryTemplate retry = new RetryTemplate();

	{
		retry.setBackOffPolicy(new ExponentialBackOffPolicy());
	}

	@Test
	public void contextLoads(CapturedOutput output) throws Exception {
		assertThat(retry.execute(context -> output.getErr().contains("bar"))
				.booleanValue()).isTrue();
		assertThat(output.getErr()).doesNotContain("foo");
	}

[wilkinsona]

For a test involving multiple threads, there's a race condition between the first and second assertion. I wonder if an API that calls the supplier repeatedly until a condition is met, and then passes the same value from the supplier for further checks would be better? Here's a simplified example that ignores timeout/back-off etc:

@Test
void example() {
	await(this.output::getOut, (out) -> out.contains("bar"), (out) -> assertThat(out).contains("foo"));
}

public static <T> void await(Supplier<T> supplier, Predicate<T> predicate, Consumer<T> consumer) {
	T value = supplier.get();
	while (!predicate.test(value)) {
		value = supplier.get();
	}
	consumer.accept(value);
}

This feels like a general purpose testing utility rather than something that should be coupled to output capture. As such, it feels better suited to being in JUnit, AssertJ, or even Framework.

[wilkinsona]

And now that my memory has stopped failing me, this is what Awaitility does, just with slightly different syntax. I think we'd be reinventing (part of) the wheel if we did anything here.

[dsyer]

Or you could fold the Consumer into the test by just asserting on the result:

@Test
void example() {
	 assertThat(await(this.output::getOut, (out) -> out.contains("bar")).contains("foo");
}

public static <T> T await(Supplier<T> supplier, Predicate<T> predicate, Consumer<T> consumer) {
	T value = supplier.get();
	while (!predicate.test(value)) {
		// omit timeout and backoff
		value = supplier.get();
	}
	return value;
}

[wilkinsona]

Yep. FWIW, that's exactly what Awaitility does. See <T> T until(Callable<T> supplier, Predicate<? super T> predicate) for example.

[dsyer]

Any chance we could use Awaitility in Boot, so we can get the dependency version in our BOM?

[wilkinsona]

We can certainly consider it. We do have some tests where it would be useful, for example:

• spring-boot/spring-boot-tests/spring-boot-integration-tests/spring-boot-devtools-tests/src/test/java/org/springframework/boot/devtools/tests/DevToolsIntegrationTests.java

  Lines 194 to 215 in 1f280e3

  	private int awaitServerPort() throws Exception {
  	Duration timeToWait = Duration.ofSeconds(40);
  	long end = System.currentTimeMillis() + timeToWait.toMillis();
  	System.out.println("Reading server port from '" + this.serverPortFile + "'");
  	while (this.serverPortFile.length() == 0) {
  	if (System.currentTimeMillis() > end) {
  	throw new IllegalStateException(String.format(
  	"server.port file '" + this.serverPortFile + "' was not written within " + timeToWait.toMillis()
  	+ "ms. Application output:%n%s%s",
  	FileCopyUtils.copyToString(new FileReader(this.launchedApplication.getStandardOut())),
  	FileCopyUtils.copyToString(new FileReader(this.launchedApplication.getStandardError()))));
  	}
  	Thread.sleep(100);
  	}
  	FileReader portReader = new FileReader(this.serverPortFile);
  	int port = Integer.valueOf(FileCopyUtils.copyToString(portReader));
  	this.serverPortFile.delete();
  	System.out.println("Got port " + port);
  	this.launchedApplication.restartRemote(port);
  	Thread.sleep(1000);
  	return port;
  	}

• spring-boot/spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-integration/src/test/java/smoketest/integration/consumer/SampleIntegrationApplicationTests.java

  Lines 83 to 114 in 1f280e3

  	private String getOutput(File outputDir) throws Exception {
  	Future<String> future = Executors.newSingleThreadExecutor().submit(new Callable<String>() {
  	@Override
  	public String call() throws Exception {
  	Resource[] resources = getResourcesWithContent(outputDir);
  	while (resources.length == 0) {
  	Thread.sleep(200);
  	resources = getResourcesWithContent(outputDir);
  	}
  	StringBuilder builder = new StringBuilder();
  	for (Resource resource : resources) {
  	try (InputStream inputStream = resource.getInputStream()) {
  	builder.append(new String(StreamUtils.copyToByteArray(inputStream)));
  	}
  	}
  	return builder.toString();
  	}
  	});
  	return future.get(30, TimeUnit.SECONDS);
  	}
  	private Resource[] getResourcesWithContent(File outputDir) throws IOException {
  	Resource[] candidates = ResourcePatternUtils.getResourcePatternResolver(new DefaultResourceLoader())
  	.getResources("file:" + outputDir.getAbsolutePath() + "/**");
  	for (Resource candidate : candidates) {
  	if ((candidate.getFilename() != null && candidate.getFilename().endsWith(".writing"))
  	|| candidate.contentLength() == 0) {
  	return new Resource[0];
  	}
  	}
  	return candidates;
  	}