HorizontalPagerScrollingContentTest.kt

/*
 * Copyright 2021 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
 *
 *      https://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.google.accompanist.pager

import androidx.compose.foundation.background
import androidx.compose.foundation.horizontalScroll
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.BoxWithConstraints
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.fillMaxHeight
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.width
import androidx.compose.foundation.rememberScrollState
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Brush
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.platform.LocalDensity
import androidx.compose.ui.platform.testTag
import androidx.compose.ui.test.junit4.createComposeRule
import androidx.compose.ui.test.onNodeWithTag
import androidx.compose.ui.unit.dp
import androidx.test.ext.junit.runners.AndroidJUnit4
import com.google.common.truth.Truth.assertThat
import org.junit.Rule
import org.junit.Test
import org.junit.runner.RunWith

@OptIn(ExperimentalPagerApi::class) // Pager is currently experimental
@RunWith(AndroidJUnit4::class)
class HorizontalPagerScrollingContentTest {
    @get:Rule
    val rule = createComposeRule()

    @Test
    fun horizontalPagerScrollingContentTest() {
        val pagerState = PagerState()

        rule.setContent {
            HorizontalPager(
                count = 2,
                state = pagerState,
                modifier = Modifier.fillMaxSize().testTag(TestTag)
            ) { page ->
                BoxWithConstraints(Modifier.fillMaxWidth()) {
                    // We make the scrolling Row content 2x the width, so that it scrolls
                    val width = with(LocalDensity.current) { (constraints.maxWidth * 2).toDp() }

                    Row(Modifier.horizontalScroll(rememberScrollState())) {
                        val background = if (page == 0) Color.Green else Color.Red

                        Box(
                            Modifier
                                .fillMaxHeight()
                                .width(width)
                                .background(
                                    brush = Brush.horizontalGradient(
                                        listOf(background, Color.Black)
                                    )
                                )
                        )
                    }
                }
            }
        }

        // Perform a very quick, high velocity scroll which will scroll the inner content to its
        // opposite/end edge
        rule.onNodeWithTag(TestTag)
            .swipeAcrossCenterWithVelocity(velocityPerSec = 2_000.dp, distancePercentageX = -0.5f)

        // Wait for the flings to end
        rule.waitForIdle()

        // Assert that we're still on page 0
        assertThat(pagerState.currentPage).isEqualTo(0)
        assertThat(pagerState.currentPageOffset).isWithin(0.01f).of(0f)

        // Perform a scroll in the same direction again
        rule.onNodeWithTag(TestTag)
            .swipeAcrossCenterWithVelocity(velocityPerSec = 2_000.dp, distancePercentageX = -0.6f)

        // Wait for the flings to end
        rule.waitForIdle()

        // Assert that we're now on page 1
        assertThat(pagerState.currentPage).isEqualTo(1)
        assertThat(pagerState.currentPageOffset).isWithin(0.01f).of(0f)
    }

    companion object {
        const val TestTag = "Pager"
    }
}