Kotlin equivalent of Swift Expectations/Promises

Question

I am trying to write some UnitTests for my native mobile applications, but have ran into a roadblock in my Android Tests. Specifically, I am struggling to find an example of Kotlin's version of Swift's Expectations/Promises..

I've found examples of Kotlin Promises, but they seem to be way more complicated than needed...

For example, here is a test for the login API function in my iOS project:

func testLogin() {

    /// Prepare for login
    if CURRENT_USER != nil {
        logout()
    }

    /// Login
    let promise = expectation(description: "User is logged in.")

    // 1. Given
    var isSuccess: Bool = false

    // 2. When
    User.login(username: maleUsername, password: malePassword, success: {
        isSuccess = true
        promise.fulfill()
    }) { (_, agreeToTerms) in
        XCTFail()
    }
    wait(for: [promise], timeout: maxTimeOut)

    // 3. Then
    XCTAssertNotNil(CURRENT_USER)
    XCTAssertTrue(isSuccess)

    /// Logout
    logout()
}

This is pretty simple to me. I have an asynchronous method login that has two possible completion blocks: success and failure; and I need to wait for one of them to complete before evaluating. To do this, I create a promise before the call, then I fulfill the promise in the two completion blocks, and I wait for the promise to fulfill before running my assertions.

Now in Kotlin, I have a similar test:

private val loginFragment = LoginFragment()

@Test
fun loginTest() {

    val username = ""
    val password = ""

    // TODO: Create Promise

    loginFragment.loginViewModel
            .login(username, password)
            .observe(loginFragment, Observer {
                loginFragment.activity?.onResult(it?.result,

                        onSuccess = {
                            // TODO: Fill Promise
                        },
                        onValidationError = {
                            // TODO: Fail Test
                        })
            })

    // TODO: Assertions

}

But I can't find an equivalent of swift's promises..

Does one exist in Kotlin? If not, how would I implement a version of my Swift's testLogin method in Kotlin?

Answer 1

You can use Kotlin coroutines, for example:

@Test
fun loginTest() {
    val result = runBlocking {
        val loginResult = login() 
        loginResult
    }
    if (result == "Success") {
        // do your work when Success
    } else {
        // do your work when Error
    }
}
suspend fun login(): String = suspendCoroutine { continuation ->
    val username = ""
    val password = ""
    loginFragment.loginViewModel
    .login(username, password)
    .observe(loginFragment, Observer {
        loginFragment.activity?.onResult(it?.result,

                    onSuccess = {
                        continuation.resume("Success")
                    },
                    onValidationError = {
                        continuation.resume("Error") // take a look for other methods, e.g. resumeWithException(exception)

                    })
    })   
}

To use coroutines you need to add next lines to app's build.gradle file dependencies:

final KOTLIN_COROUTINES_VERSION = '1.0.1'
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$KOTLIN_COROUTINES_VERSION"

Hope it will help.