How do I test a suspend function using mockk objects and junit.jupiter?

kotlin junit-jupiter ktor mockk

I am building a Kotlin Slack Event API app using Ktor, but I'm having some trouble testing my function.

I have a class called SlackApi that, among other things, will use the KTor client to request the list of users from the Slack API.

import com.google.gson.Gson
import io.ktor.client.HttpClient
import io.ktor.client.engine.cio.CIO
import io.ktor.client.request.HttpRequestBuilder
import io.ktor.client.request.get
import io.ktor.client.request.header
import io.ktor.client.request.url
import io.ktor.client.statement.HttpResponse
import io.ktor.client.statement.readText
import io.ktor.http.HttpHeaders

data class SlackUserProfile(val real_name: String, val display_name: String, val real_name_normalized:String, val display_name_normalized: String)
data class SlackUser(val id: String, val profile: SlackUserProfile)
data class UserListResponse(val ok: Boolean, val members: List<SlackUser>)

class SlackApi(
    private val client: HttpClient = HttpClient(CIO),
    private val gson: Gson = Gson(),
    private val bot_user_oauth_token: String = "bot-oauth-token-goes-here",
) {
    suspend fun getUsers(): UserListResponse {
        var builder = HttpRequestBuilder()
        builder.url("https://slack.com/api/users.list")
        builder.header(HttpHeaders.Authorization, "Bearer ${bot_user_oauth_token}")
        val response = client.get<HttpResponse>(builder)
        return gson.fromJson(response.readText(), UserListResponse::class.java)
    }
}

I have a (nonworking) attempt at a test:

import com.google.gson.Gson
import io.ktor.client.HttpClient
import io.ktor.client.request.HttpRequestBuilder
import io.ktor.client.request.get
import io.ktor.client.statement.HttpResponse
import io.ktor.client.statement.readText
import io.mockk.coEvery
import io.mockk.mockk
import kotlinx.coroutines.test.runBlockingTest
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Nested
import org.junit.jupiter.api.Test

class SlackApiTest {
    private val client:HttpClient = mockk()
    private val botToken: String = "123456-bottoken"
    private val testObj = SlackApi(
        client = client,
        bot_user_oauth_token = botToken,
    )

    @Nested
    inner class GetUsers {

        @Test
        fun `returns the list of users from the client`() = runBlockingTest {
            val expectedUsers = listOf(SlackUser("blarg", SlackUserProfile("name", "name", "name", "name")))
            val jsonUsers:String = Gson().toJson(expectedUsers)

            var httpResponse:HttpResponse = mockk()
            coEvery { httpResponse.readText() } returns jsonUsers

            val builder = slot<HttpRequestBuilder>()

            coEvery { client.get<HttpResponse>(capture(builder))
            } coAnswers {
                assertEquals("https://slack.com/api/users.list", builder.captured.url)
                assertEquals("Bearer ${botToken}", builder.captured.headers.get(HttpHeaders.Authorization))
                httpResponse
            }

            val allUsers = testObj.getUsers()

            assertEquals(expectedUsers, allUsers.members)
        }
    }
}

But this doesn't work, and it's likely because of some misunderstanding I have with how this training should work. Instead I get a stacktrace error:

java.io.EOFException: Premature end of stream: expected 1 bytes

    at io.ktor.utils.io.core.StringsKt.prematureEndOfStream(Strings.kt:492)
    at io.ktor.utils.io.core.internal.UnsafeKt.prepareReadHeadFallback(Unsafe.kt:78)
    at io.ktor.utils.io.core.internal.UnsafeKt.prepareReadFirstHead(Unsafe.kt:61)
    at io.ktor.utils.io.charsets.CharsetJVMKt.decode(CharsetJVM.kt:556)
    at io.ktor.utils.io.charsets.EncodingKt.decode(Encoding.kt:103)
    at io.ktor.utils.io.charsets.EncodingKt.decode$default(Encoding.kt:101)
    at io.ktor.client.statement.HttpStatementKt.readText(HttpStatement.kt:173)
    at io.ktor.client.statement.HttpStatementKt.readText$default(HttpStatement.kt:168)
    at my.slackbot.SlackApiTest$GetUsers$returns the list of users from the client$1$1.invokeSuspend(SlackApiTest.kt:33)
    at my.slackbot.SlackApiTest$GetUsers$returns the list of users from the client$1$1.invoke(SlackApiTest.kt)
    at io.mockk.impl.eval.RecordedBlockEvaluator$record$block$2$1.invokeSuspend(RecordedBlockEvaluator.kt:26)
    at io.mockk.impl.eval.RecordedBlockEvaluator$record$block$2$1.invoke(RecordedBlockEvaluator.kt)
    at io.mockk.InternalPlatformDsl$runCoroutine$1.invokeSuspend(InternalPlatformDsl.kt:20)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:274)
    at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:86)
    at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:61)
    at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)
    at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt)
    at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)
    at io.mockk.InternalPlatformDsl.runCoroutine(InternalPlatformDsl.kt:19)
    at io.mockk.impl.eval.RecordedBlockEvaluator$record$block$2.invoke(RecordedBlockEvaluator.kt:26)
    at io.mockk.impl.eval.RecordedBlockEvaluator$enhanceWithRethrow$1.invoke(RecordedBlockEvaluator.kt:74)
    at io.mockk.impl.recording.JvmAutoHinter.autoHint(JvmAutoHinter.kt:23)
    at io.mockk.impl.eval.RecordedBlockEvaluator.record(RecordedBlockEvaluator.kt:36)
    at io.mockk.impl.eval.EveryBlockEvaluator.every(EveryBlockEvaluator.kt:30)
    at io.mockk.MockKDsl.internalCoEvery(API.kt:98)
    at io.mockk.MockKKt.coEvery(MockK.kt:116)
    at my.slackbot.SlackApiTest$GetUsers$returns the list of users from the client$1.invokeSuspend(SlackApiTest.kt:33)
    at my.slackbot.SlackApiTest$GetUsers$returns the list of users from the client$1.invoke(SlackApiTest.kt)
    at kotlinx.coroutines.test.TestBuildersKt$runBlockingTest$deferred$1.invokeSuspend(TestBuilders.kt:50)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at kotlinx.coroutines.test.TestCoroutineDispatcher.dispatch(TestCoroutineDispatcher.kt:50)
    at kotlinx.coroutines.internal.DispatchedContinuationKt.resumeCancellableWith(DispatchedContinuation.kt:305)
    at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:30)
    at kotlinx.coroutines.BuildersKt__Builders_commonKt.startCoroutineImpl(Builders.common.kt:192)
    at kotlinx.coroutines.BuildersKt.startCoroutineImpl(Unknown Source)
    at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:145)
    at kotlinx.coroutines.BuildersKt__Builders_commonKt.async(Builders.common.kt:91)
    at kotlinx.coroutines.BuildersKt.async(Unknown Source)
    at kotlinx.coroutines.BuildersKt__Builders_commonKt.async$default(Builders.common.kt:84)
    at kotlinx.coroutines.BuildersKt.async$default(Unknown Source)
    at kotlinx.coroutines.test.TestBuildersKt.runBlockingTest(TestBuilders.kt:49)
    at kotlinx.coroutines.test.TestBuildersKt.runBlockingTest$default(TestBuilders.kt:45)
    at my.slackbot.SlackApiTest$GetUsers.returns the list of users from the client(SlackApiTest.kt:28)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:686)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
    at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
    at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:212)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:208)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:137)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:71)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:248)
    at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$5(DefaultLauncher.java:211)
    at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:226)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:199)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:132)
    at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)

I need to be able to test the behavior of this function, but I can't find any documentation that details what I'm trying to do or if it's even possible.


Solution 1:

The exception occurs because function httpResponse.readText() hasn't been mocked on this line:

coEvery { httpResponse.readText() } returns jsonUsers

readText() is an extension function on HttpResponse and it has to be mocked using mockkStatic function, for example like this:

@BeforeEach
fun setup() {
    mockkStatic(HttpResponse::readText)
}

setup() will be executed before each @Test, because it is marked with @BeforeEach annotation.

Solution 2:

You can use the Ktor's MockEngine to test response transformation and request headers:

@Test
fun `returns the list of users from the client`(): Unit = runBlocking {
    val expectedUsers = listOf(SlackUser("blarg", SlackUserProfile("name", "name", "name", "name")))
    val expectedResponse = UserListResponse(true, expectedUsers)
    val jsonResponse: String = Gson().toJson(expectedResponse)

    val client = HttpClient(MockEngine) {
        engine {
            addHandler { request ->
                assertEquals(request.url.toString(), "https://slack.com/api/users.list")
                assertEquals(request.headers["Authorization"], "Bearer 123456-bottoken")
                respond(content = jsonResponse)
            }
        }
    }

    val testObj = SlackApi(
        client = client,
        bot_user_oauth_token = "123456-bottoken",
    )

    assertEquals(expectedUsers,  testObj.getUsers().members)
}

Unfortunately, I didn't find a way to solve your problem using the mockk library because of the weird Premature end of stream: expected 1 bytes error you described and the presence of top-level inline methods in the HttpClient class.

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