StateFlowHandlerTest with a couple of tests cases that pass correctly for StateFlow

StateFlowHandlerTest.kt

/*
 * Copyright (C) 2020 Raul Hernandez Lopez
 *
 * 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
 * limitations under the License.
 */
package com.raulh82vlc.tweetsearch.search.ui

import com.nhaarman.mockitokotlin2.mock
import com.nhaarman.mockitokotlin2.verify
import com.nhaarman.mockitokotlin2.whenever
import com.raulh82vlc.tweetsearch.common.threading.TaskThreading
import com.raulh82vlc.tweetsearch.search.addTweets
import com.raulh82vlc.tweetsearch.search.data.datasource.db.model.Tweet
import com.raulh82vlc.tweetsearch.search.data.datasource.db.model.TweetsUIState
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.test.TestCoroutineDispatcher
import org.junit.After
import org.junit.Before
import org.junit.Test

@ExperimentalCoroutinesApi
class StateFlowHandlerTest {

    private val testDispatcher = TestCoroutineDispatcher()
    private val taskThreading: TaskThreading = mock()
    private val stateFlow = MutableStateFlow<TweetsUIState?>(null)
    private val fragment: SearchTweetFragment = mock()
    private lateinit var stateFlowHandler: StateFlowHandler

    private fun getStateFlow(): StateFlow<TweetsUIState?> = stateFlow

    @Before
    fun before() {
        whenever(taskThreading.ui()).thenReturn(testDispatcher)
        stateFlowHandler = StateFlowHandler(taskThreading)
    }

    @After
    fun tearDown() {
        testDispatcher.cleanupTestCoroutines()
    }

    @Test
    fun `show Loading UI state`() = runBlockingTest {
        // set value for stateflow with a loading state
        stateFlow.value = TweetsUIState.LoadingUIState
        // process state collection
        stateFlowHandler.processStateCollection(getStateFlow(), fragment)
        // verify loader shows
        verify(fragment).showLoader()
    }

    @Test
    fun `show List results UI state`() = runBlockingTest {
        // set value for stateFlow with a state with tweets
        val tweets: List<Tweet> = addTweets()
        stateFlow.value = TweetsUIState.ListResultsUIState(tweets)
        // process state collection for a filled list
        stateFlowHandler.processStateCollection(getStateFlow(), fragment)
        // verify list is updated and shows, rest is hidden
        verify(fragment).hideLoader()
        verify(fragment).hideError()
        verify(fragment).showList()
        verify(fragment).updateList(tweets)
        verify(fragment).showAnimation()
    }
}