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Roger Viñas Alcon for Adevinta Spain

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Testing with @WireMockTest

WireMock is a great library to mock APIs in your tests and supports Junit5 with two modes:

  • Declarative with @WireMockTest
  • Programmatic with WireMockExtension

But "talk is cheap, show me the code ..." 😮

Ok so let's implement this scenario:

Diagram

GitHub logo rogervinas / wiremock-testing

🤹 WireMock Testing

BarClient

BarClient interface

interface BarClient {

  fun call(name: String): String
}
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BarKtorClient test

I will use a Ktor client for no other reason that I need an Http client and this seems interesting, as we are using Kotlin.

So a simple @WireMockTest for the BarKtorClient looks like:

@WireMockTest
class BarKtorClientShould {

 private val name = "Sue"

 @Test
 fun `call bar api`(wm: WireMockRuntimeInfo) {
  stubFor(
   get(urlPathMatching("/bar/$name"))
   .willReturn(ok().withBody("Hello $name I am Bar!"))
  )

  assertThat(
    BarKtorClient(wm.httpBaseUrl).call(name)
  ).isEqualTo("Hello $name I am Bar!")
 }

 @Test
 fun `handle bar api server error`(wm: WireMockRuntimeInfo) {
  stubFor(
   get(urlPathMatching("/bar/.+"))
   .willReturn(serverError())
  )

  assertThat(BarKtorClient(wm.httpBaseUrl).call(name))
   .startsWith("Bar api error: Server error")
 }
}
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BarKtorClient implementation

In order to make the test pass 🟩 we can implement the BarKtorClient this way:

class BarKtorClient(private val url: String) : BarClient {

 private val client = HttpClient(CIO)

 override fun call(name: String): String = runBlocking {
  try {
   client.get("$url/bar/$name")
  } catch (e: Exception) {
   "Bar api error: ${e.message}"
  }
 }
}
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FooClient

FooClient interface

interface FooClient {

  fun call(name: String): String
}
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FooKtorClient test

For this test I want to use WireMock's response templating feature, so I will register a WireMockExtension instead of using @WireMockTest:

@TestInstance(PER_CLASS)
class FooKtorClientShould {

 private val name = "Joe"

 @RegisterExtension
 val wm: WireMockExtension = WireMockExtension.newInstance()
  .options(wireMockConfig()
    .extensions(ResponseTemplateTransformer(true))
  )
  .configureStaticDsl(true)
  .build()

 @Test
 fun `call foo api`() {
  stubFor(
   get(urlPathEqualTo("/foo"))
   .withQueryParam("name", matching(".+"))
   .willReturn(ok().withBody("Hello {{request.query.name}} I am Foo!"))
  )

  assertThat(FooKtorClient(wm.baseUrl()).call(name))
   .isEqualTo("Hello $name I am Foo!")
 }

 @Test
 fun `handle foo api server error`() {
  stubFor(
   get(urlPathEqualTo("/foo"))
   .willReturn(WireMock.serverError())
  )

  assertThat(FooKtorClient(wm.baseUrl()).call(name))
   .startsWith("Foo api error: Server error")
 }
}
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Note that:

  • Instead of having a fixed response, with WireMock's response templating we can insert in the response values from the request. In this case the query parameter name.
  • @TestInstance(PER_CLASS) makes JUnit5 create a single instance of FooKtorClientShould to be used by both tests so the WireMockExtension is registered only once. By default JUnit5 would create one instance for each test (see Test Instance Lifecycle).
  • configureStaticDsl(true) makes it possible to use the static DSL, that is using stubFor(...) staticly instead of wm.stubFor(...).

FooKtorClient implementation

Same as before in order to make the test pass 🟩 we can implement the FooKtorClient this way:

class FooKtorClient(private val url: String) : FooClient {

 private val client = HttpClient(CIO)

 override fun call(name: String): String = runBlocking {
  try {
   client.get("$url/foo") {
    parameter("name", name)
   }
  } catch (e: Exception) {
   "Foo api error: ${e.message}"
  }
 }
}
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AppUseCase

Now we have to implement AppUseCase, which will use a FooClient to call the Foo API and then a BarClient to call the Bar API.

As it is not WireMock related because we can test first the implementation just using MockK JUnit5 extension we can skip the details and you can review the source code of AppUseCaseShould and AppUseCase.

App

App implementation

Let me introduce first the App implementation, as I will present later two different types of WireMock tests:

class App(
 private val name: String,
 private val fooApiUrl: String,
 private val barApiUrl: String
) {

 fun execute() = AppUseCase().execute(
  name,
  FooKtorClient(fooApiUrl),
  BarKtorClient(barApiUrl)
 )
}
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App test with @WireMockTest

Since in this example Foo API and Bar API do not have conflicting endpoints, we can use one @WireMockTest to mock both APIs:

@WireMockTest
class AppShouldWithOneWireMockTest {

 private val name = "Ada"

 @Test
 fun `call foo and bar`(wm: WireMockRuntimeInfo) {
  stubFor(
   get(urlPathEqualTo("/foo"))
    .withQueryParam("name", equalTo(name))
    .willReturn(ok().withBody("Hello $name I am Foo!"))
  )
  stubFor(
   get(urlPathMatching("/bar/$name"))
    .willReturn(ok().withBody("Hello $name I am Bar!"))
  )

  val app = App(name, wm.httpBaseUrl, wm.httpBaseUrl)

  assertThat(app.execute()).isEqualTo(
   """
    Hi! I am $name
    I called Foo and its response is Hello $name I am Foo!
    I called Bar and its response is Hello $name I am Bar!
    Bye!
   """.trimIndent()
  )
 }
}
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App test with WireMockExtension

But imagine a real scenario where Foo API and Bar API do have conflicting endpoints, or you just want to mock them separatedly for any reason. In this case you can register two WireMockExtensions instead of using @WireMockTest:

@TestInstance(PER_CLASS)
class AppShouldWithTwoWireMockExtensions {

 private val name = "Leo"

 @RegisterExtension
 val wireMockFoo: WireMockExtension = newInstance().build()

 @RegisterExtension
 val wireMockBar: WireMockExtension = newInstance().build()

 @Test
 fun `call foo and bar`() {
  wireMockFoo.stubFor(
   get(WireMock.urlPathEqualTo("/foo"))
    .withQueryParam("name", equalTo(name))
    .willReturn(ok().withBody("Hello $name I am Foo!"))
  )
  wireMockBar.stubFor(
   get(WireMock.urlPathMatching("/bar/$name"))
    .willReturn(ok().withBody("Hello $name I am Bar!"))
  )

  val app = App(name, wireMockFoo.baseUrl(), wireMockBar.baseUrl())

  assertThat(app.execute()).isEqualTo(
   """
    Hi! I am $name
    I called Foo and its response is Hello $name I am Foo!
    I called Bar and its response is Hello $name I am Bar!
    Bye!
   """.trimIndent()
  )
 }
}
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That was a good one! Happy coding! 💙

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