Wiremock: Now with extension points (open source == awesome)

I have been using Wiremock as my preferred HTTP test double for some time now. I think it is a fantastic tool and I mentioned it quite a lot at a talk I gave at Skills matter and it turned out the author, Tom Akehurst, was in the audience.

Shamefully I had a private fork of Wiremock at the company I worked for, we'd hacked away at it and added support for copying our platform headers, adding our HMAC signatures to responses etc. We'd also used it for load testing and made a bunch of the Jetty tuning options configurable. Some of this, HMAC, was confidential, 90% not so much :)

So over the Christmas holidays, with the help of Tom, I've been hacking away with Wiremock, and the new release now contains:

• Configurable number of container threads
• Exposed Jetty tuning options: Acceptor threads & Accept queue size
• Extension points

The first two were my PRs, the latter was by Tom, who (rightly) rejected my PR as it added too much latency to start up as it was reflection based. But kindly Tom hashed out an alternative documented here: https://github.com/tomakehurst/wiremock/issues/214

If you've used Wiremock before you'll know you run/interact it in two modes: via its Java API and as a standalone process. This means you can use it for unit/integration testing and black box acceptance testing. Let's look with the Java API, how to use this feature in standalone mode is documented on the Wiremock site:

	public abstract class ResponseTransformer implements Extension {
	public abstract ResponseDefinition transform(Request request, ResponseDefinition responseDefinition, FileSource files);
	public boolean applyGlobally() {
	return true;
	}
	}

view raw ResponseTransformer.java hosted with ❤ by GitHub

This is the class you extend to extend Wiremock and here is a simple implementation that copies over headers that begin with Batey, this example is inspired by a platform requirement to copy over all platform headers when dealing with requests.

	@Override
	public ResponseDefinition transform(Request request, ResponseDefinition responseDefinition, FileSource files) {
	HttpHeaders stubbedResponseHeaders = responseDefinition.getHeaders();
	Collection<HttpHeader> responseHeaders = stubbedResponseHeaders == null ? new ArrayList<HttpHeader>() : stubbedResponseHeaders.all();
	Set<String> allHeaderKeys = request.getAllHeaderKeys();
	for (String headerName : allHeaderKeys) {
	if (headerName.startsWith("Batey")) {
	responseHeaders.add(new HttpHeader(headerName, request.getHeader(headerName)));
	}
	}
	responseDefinition.setHeaders(new HttpHeaders(responseHeaders));
	return responseDefinition;
	}
	@Override
	public String name() {
	return "CopiesBateyHeaders";
	}

view raw CopiesBateyHeaders.java hosted with ❤ by GitHub

Simple! Now to use it from the Java API you add the following to your stubbing:

	stubFor(get(urlEqualTo("/batey-service"))
	.willReturn(aResponse()
	.withStatus(200)
	.withBody("Original body")
	.withTransformers("CopiesBateyHeaders")));

view raw Example Stubbing hosted with ❤ by GitHub

The name, CopiesBateyHeaders, in your implementation needs to match the stubbing. We can now test a piece of code that looks like this:

	public void callBatey() throws IOException {
	HttpResponse httpResponse = Request.Get(host + "/batey-service")
	.addHeader("Batey-Auth", "super-token")
	.execute().returnResponse();
	Header authHeader = httpResponse.getFirstHeader("Batey-Auth");
	if (authHeader == null) {
	throw new NoBateyAuthHeader();
	}
	}

view raw AwesomeHttpClient.java hosted with ❤ by GitHub

For both cases: When the dependency does copy the header over and when it doesn't. Here is the test for does:

	@Test
	public void shouldForwardAuthHeaders() throws Exception {
	//given
	stubFor(get(urlEqualTo("/batey-service"))
	.willReturn(aResponse()
	.withStatus(200)
	.withBody("Original body")
	.withTransformers("CopiesBateyHeaders")));
	AwesomeHttpClient awesomeHttpClient = new AwesomeHttpClient("http://localhost:8089");
	//when
	awesomeHttpClient.callBatey();
	//then
	verify(getRequestedFor(urlEqualTo("/batey-service"))
	.withHeader("Batey-Auth", equalTo("super-token")));
	}

view raw CopiesHeader.java hosted with ❤ by GitHub

And doesn't:

	@Test(expected = NoBateyAuthHeader.class)
	public void throwsExceptionIfNoAuthHeaderReturned() throws Exception {
	//given
	stubFor(get(urlEqualTo("/batey-service"))
	.willReturn(aResponse()
	.withStatus(200)
	.withBody("Original body")));
	// .withTransformers("CopiesBateyHeaders"))); // no auth header copying this time
	AwesomeHttpClient awesomeHttpClient = new AwesomeHttpClient("http://localhost:8089");
	//when
	awesomeHttpClient.callBatey();
	//then - exception expected
	}

view raw NoCopyHeaders.java hosted with ❤ by GitHub

Now you're probably thinking we could have just primed this right?

Well I hate noise in tests, and we want a single test making sure we throw an error if the header isn't copied but for all the rest of the behaviour (obviously there isn't any in this example) we can now forget about the fact our dependency should copy the headers, thus reducing noise in the priming of all our other tests.

I find this particularly important in black box acceptance tests, which often get very noisy.

I love open source :) All the code for this example is on my github here.