Testing suspending functions for exception with JUnit5 assertThrows and MockWebServer

Question

How can we test a suspending function with MockWebServer that supposed to throw exception?

fun `Given Server down, should return 500 error`()= testCoroutineScope.runBlockingTest {

    // GIVEN
    mockWebServer.enqueue(MockResponse().setResponseCode(500))

    // WHEN
    val exception = assertThrows<RuntimeException> {
        testCoroutineScope.async {
            postApi.getPosts()
        }

    }

    // THEN
    Truth.assertThat(exception.message)
        .isEqualTo("com.jakewharton.retrofit2.adapter.rxjava2.HttpException: HTTP 500 Server Error")
}

Calling postApi.getPosts() directly inside assertThrows is not possible since it's not a suspending function, i tried using async, launch and

 val exception = testCoroutineScope.async {
            assertThrows<RuntimeException> {
                launch {
                    postApi.getPosts()
                }
            }
        }.await()

but test fails with org.opentest4j.AssertionFailedError: Expected java.lang.RuntimeException to be thrown, but nothing was thrown. for each variation.

score 8 · Answer 1 · edited Sep 13 '20 at 07:29

8

fun `Given Server down, should return 500 error`()= testCoroutineScope.runBlockingTest {

    // GIVEN
    mockWebServer.enqueue(MockResponse().setResponseCode(500))

    // WHEN
     val result = runCatching {
               postApi.getPosts() 
            }.onFailure {
                assertThat(it).isInstanceOf(###TYPE###::class.java)
            }

    
           
    // THEN
    assertThat(result.isFailure).isTrue()
    Truth.assertThat(exception?.message)
        .isEqualTo("com.jakewharton.retrofit2.adapter.rxjava2.HttpException: HTTP 500 Server Error")
}

edited Sep 13 '20 at 07:29

David Buck

3,752
35
31
35

answered Sep 13 '20 at 04:52

chandima

81
1
2

I prefer this version, although both solutions are good – mez.pahlan Oct 19 '21 at 15:24

score 2 · Accepted Answer · answered Jun 03 '20 at 08:00

You could just remove the assertThrows, using something like this:

fun `Given Server down, should return 500 error`()= testCoroutineScope.runBlockingTest {

    // GIVEN
    mockWebServer.enqueue(MockResponse().setResponseCode(500))

    // WHEN
    val exception = try {
        postApi.getPosts()
        null
    } catch (exception: RuntimeException){
        exception
    }

    // THEN
    Truth.assertThat(exception?.message)
        .isEqualTo("com.jakewharton.retrofit2.adapter.rxjava2.HttpException: HTTP 500 Server Error")
}

Testing suspending functions for exception with JUnit5 assertThrows and MockWebServer

2 Answers2