Introduce TestScope.collectLastValue(Flow)

/*

 * Copyright (C) 2022 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

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package com.android.systemui.coroutines

import kotlin.coroutines.CoroutineContext

import kotlin.coroutines.EmptyCoroutineContext

import kotlinx.coroutines.CoroutineStart

import kotlinx.coroutines.Job

import kotlinx.coroutines.flow.Flow

import kotlinx.coroutines.launch

import kotlinx.coroutines.test.TestScope

import kotlinx.coroutines.test.runCurrent

/** Collect [flow] in a new [Job] and return a getter for the last collected value. */

fun <T> TestScope.collectLastValue(

    flow: Flow<T>,

    context: CoroutineContext = EmptyCoroutineContext,

    start: CoroutineStart = CoroutineStart.DEFAULT,

): () -> T? {

    var lastValue: T? = null

    backgroundScope.launch(context, start) { flow.collect { lastValue = it } }

    return {

        runCurrent()

        lastValue

    }

}