kotlin + retrofit + coroutine + androidTest

Issue

How can create androidTest for sample retrofit request?

Sample

data class TestDataClass(
    val id: String,
    val employee_name: String,
    val employee_salary: String,
    val employee_age: String,
    val profile_image: String)

enum class NetworkState { LOADING, ERROR, DONE }

private const val BASE_URL = "http://dummy.restapiexample.com/api/v1/"

private val moshi = Moshi.Builder()
    .add(KotlinJsonAdapterFactory())
    .build()



private val retrofit = Retrofit.Builder()
    .addConverterFactory(MoshiConverterFactory.create(moshi))
    .addCallAdapterFactory(CoroutineCallAdapterFactory())
    .baseUrl(BASE_URL)
    .build()

interface TestApiService {
    @GET("employees")
    fun getPropertiesAsync():
            Deferred<List<TestDataClass>>
}

object TestApi {
    val retrofitTest : TestApiService by lazy { retrofit.create(TestApiService::class.java) }
}

Solution

You can use the MockWebServer library by Square.

Create a resources in your tests source set (src/test/resources), and put in it a JSON file containing a sample response from your API. Let's say it looks like this:

src/test/resources/sample_response.json

[
  {
    "id": "1",
    "employee_name": "John Doe",
    "employee_salary": "60000",
    "employee_age": 37,
    "profile_image": "https://dummy.sample-image.com/johndoe"
  }
]

You may then write your tests as:

class ApiTest {

  private lateinit var server: MockWebServer
  private lateinit var retrofit: Retrofit
  private lateinit var service: TestApiService

  @Before
  fun setup() {
    server = MockWebServer()
    retrofit = Retrofit.Builder()
        .addConverterFactory(MoshiConverterFactory.create(get<Moshi>()))
        .addCallAdapterFactory(get<CoroutinesNetworkResponseAdapterFactory>())
        .baseUrl(mockWebServer.url("/"))
        .build()
    service = retrofit.create(TestApi::class.java)
  }

  @After
  fun teardown() {
    server.close()
  }

  @Test
  fun simpleTest() = runBlocking<Unit> {
    val sampleResponse = this::class.java.getResource("/sample_response.json").readText()

    server.enqueue(
      MockResponse()
        .setBody(sampleResponse)
    )

    val response = service.getPropertiesAsync().await()

    assertTrue(1, response.size)
    assertTrue(response[0].employee_name = "John Doe"
    // Make as many assertions as you like
  }

}

You have to ask yourself though, what exactly is it that you're trying to test? There's no need to test Retrofit's functionality. Nor should you test functionality of other well known libraries like Moshi.

These tests best serve the purpose of validating that the data models you have created for API responses are indeed correct, and that your parser (in this case, Moshi) can correctly handle unexpected values (such as null) gracefully. It is therefore important that the sample responses that you pick are actual responses from your API, so that your data models can be validated against real data in tests before being used in the app.

Answered By - harold_admin