Mockative

Mocking for Kotlin/Native and Kotlin Multiplatform using the Kotlin Symbol Processing API (KSP). Notable features include:

• Concise, non-intrusive, type-safe API
• Mocking of classes and interfaces
• Supports both values and matchers when during stubbing verification
• Supports implicit stubbing of functions returning Unit

Installation for Multiplatform projects

Add the io.mockative plugin and dependency to your build.gradle.kts file:

plugins {
  id("io.mockative") version "3.2.3"
}

kotlin {
    commonMain {
        dependencies {
            implementation("io.mockative:mockative:3.2.3")
        }
    }
}

Mockative is published to Maven Central and applies the following Gradle plugins:

• com.google.devtools.ksp: Enables code generation of mockable implementations
• org.jetbrains.kotlin.plugin.allopen: Enables mocking of classes

Make sure you specify the following plugin repositories in your build.settings.kts file:

pluginManagement {
    repositories {
        gradlePluginPortal()
        google()
        mavenCentral()
    }
}

Then add the following to your gradle.properties file:

#KSP
ksp.useKSP2=true

[!TIP] Now run your tests, which will copy a set of runtime dependencies to your generated code. These will disappear whenever you run a Gradle task that is not a test, lint of other verification task, but will reappear once you run one of them again.

If you're having the following error:

KSP2: KtInvalidLifetimeOwnerAccessException: Access to invalid KtAlwaysAccessibleLifetimeToken: PSI has changed since creation

Please disable incremental processing for KSP by adding the following to your gradle.properties file:

ksp.incremental=false

Mockative 3 code generation should "just work", but if you're looking for more control over when Mockative code generation is enabled or disabled, please read Controlling generation of mocks in Mockative 3.

Making types mockable

To mock an interface or class with Mockative, annotate the type with the @Mockable annotation. This annotation tells Mockative to generate a mock implementation of the annotated type, which can be used in tests.

import io.mockative.Mockable

@Mockable
class MyService {
    // ...
}

The Kotlin all-open plugin will automatically be applied to any class annotated with @Mockable.

Mocking External Types

Sometimes we would like to mock types that are external to our module in our tests. To do so, pass a list of types you'd like to mock in any @Mockable annotation in your main module. If you add the list of types to the @Mockable annotation of a type you'd also like to mock by itself, you must specify the type itself in the list of types to mock. By not specifying any types in the annotation, a mock for the annotated type itself is generated.

import io.mockative.Mockable

@Mockable(MyService::class, Clock::class)
class MyService {
    // ...
}

Testing with Mockative

Obtaining an instance of a mock is as ease as calling the <T> mock(KClass<T>) function:

class GitHubServiceTests {
    val api = mock(of<GitHubAPI>())
}

Then, to stub a function or property on the mock you have a couple of options:

Stubbing using values

To begin stubbing a function you may simply pass the values to the function call inside a block passed to the every or coEvery (when stubbing a suspend function) functions:

// Stub a blocking function
every { githubApi.getRepository("mockative/mockative") }
    .invokes { response }

// Stub a `suspend` function (notice the use of `coEvery`)
coEvery { repositoryMapper.mapResponseToRepository(response) }
    .invokes { repository }

// Stub a property getter
every { repository.maintainer }
    .returns("Nillerr")

// Stub a property setter (these are stubbed by default)
every { repository.stars = repository.stars + 1 }
    .doesNothing()

Stubbing using matchers

Sometimes when stubbing a function we're faced with difficulties providing a specified value for one or more of the parameters of our expectation. In such cases we can use the matcher API to specify the values our stub accepts:

// Assuming we want to stub the function in this S3Client:
interface S3Client {
    suspend fun <T> getObject(input: GetObjectRequest, block: suspend (GetObjectResponse) -> T): T
}

// Providing a value for the `block` parameter is difficult, so we can use the `any()` matcher to
// specify that this expectation will match any value passed to that parameter. When we use one 
// matcher, we must use matchers for every parameter, and as such we must use the `eq(value)` 
// matcher to specify that we're expecting a specific request.
coEvery { s3Client.getObject<File>(eq(request), any()) }
    .returnsMany(expected)

Also note how we're explicitly specifying the type parameter. We could do the same by explicitly specifying it in the call to any() like this:

any<suspend (GetObjectResponse) -> File>()

But that would be significantly more verbose that the alternative.

❕Mockative has limited support for the matcher API when targeting Kotlin/Wasm (WASI).

Stubbing using functions

You may want to provide a function as an argument to another function, where you would like to be able to record invocations on that function. To do that, Mockative includes the interfaces Fun[N] and CoFun[N] (for suspend functions), each declaring a single function invoke that you can pass as a mock to other functions in order to stub and verify invocations on it:

// Declare the mock function as a property in your test class
@Mock
val block = mock(of<Fun1<GetObjectResponse, File>>())

// Stub the mock function
every { block.invoke(response) }
    .returns(file)

// Call something that calls the mock function
s3Client.getObject(request, block::invoke)

// Verify the call to the mock function
verify { block.invoke(response) }
    .wasInvoked(exactly = once)

Stubbing implementations

The following functions are available to provide a stub implementation for every expectation:

| Function | Description | |-------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | invokes(block: (args: Array<Any?>) -> R) | Invokes the specified block. The arguments passed to the block are the arguments passed to the invocation. | | invokes(block: () -> R) | Invokes the specified block. | | invokesMany(vararg block: (args: Array<Any?>) -> R) | Invokes the specified blocks in sequence. The arguments passed to the block are the arguments passed to the invocation. Once the last block in the sequence has been invoked, this stubbing will no longer match any invocation. | | invokesMany(vararg blocks: () -> R) | Invokes the specified block. Once the last block in the sequence has been invoked, this stubbing will no longer match any invocation. | | returns(value: R) | Returns the specified value. | | returnsMany(vararg value: R) | Returns the specified values in sequence. Once the last value in the sequence has been returned, this stubbing will no longer match any invocation. | | throws(throwable: Throwable) | Throws the specified exception. | | throwsMany(throwable: Throwable) | Throws the specified exceptions in sequence. Once the last exception in the sequence has been thrown, this stubbing will no longer match any invocation. |

In order to provide familiarity to developers coming from MockK, who prefer using infix notation, Mockative also supports infix notation for the invokes, returns, and throws functions:

every { api.getUsers() } returns users

When the return type of the function or property being stubbed is Unit, the following additional then function is available:

| Function | Description | |-----------------|-----------------| | doesNothing() | Returns Unit. |

Implicit stubbing of functions returning Unit

Mockative automatically stubs functions returning Unit, b