Mastering Kotlin Coroutines/

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Testing Functions Properties

Testing Functions Properties

Discover what happens during function execution when coroutines are launched.

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Testing what happens during function execution

Imagine a function that, during its execution, first shows a progress bar and then later hides it.

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suspend fun sendUserData() {
    val userData = database.getUserData()
    progressBarVisible.value = true
    userRepository.sendUserData(userData)
    progressBarVisible.value = false
}

If we only check the final result, we cannot verify that the progress bar changed its state during function execution. A helpful trick in such cases is to start this function in a new coroutine and control virtual time from outside. Notice that runTest creates a coroutine with the StandardTestDispatcher dispatcher and advances its time until idle (using the advanceUntilIdle function). This means that the children’s time will start ...