test(chat): JVM characterization tests for ChatScrollController (#1319) (#1347)

app/src/test/java/com/m57/hermescontrol/ui/chat/components/ChatScrollControllerTest.kt

@@ -0,0 +1,169 @@
+package com.m57.hermescontrol.ui.chat.components
+
+import androidx.compose.foundation.lazy.LazyListItemInfo
+import androidx.compose.foundation.lazy.LazyListLayoutInfo
+import androidx.compose.foundation.lazy.LazyListState
+import io.mockk.coEvery
+import io.mockk.coVerify
+import io.mockk.every
+import io.mockk.mockk
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.TestScope
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.runTest
+import kotlinx.coroutines.test.setMain
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class ChatScrollControllerTest {
+    private val testDispatcher = StandardTestDispatcher()
+
+    @Before
+    fun setUp() {
+        Dispatchers.setMain(testDispatcher)
+    }
+
+    @After
+    fun tearDown() {
+        Dispatchers.resetMain()
+    }
+
+    private fun mockLazyListStateAtBottom(): LazyListState {
+        val listState = mockk<LazyListState>(relaxed = true)
+        val layoutInfo = mockk<LazyListLayoutInfo>(relaxed = true)
+        val itemInfo = mockk<LazyListItemInfo>(relaxed = true)
+
+        every { layoutInfo.totalItemsCount } returns 5
+        every { layoutInfo.viewportEndOffset } returns 1000
+        every { layoutInfo.afterContentPadding } returns 0
+        every { itemInfo.index } returns 4
+        every { itemInfo.offset } returns 800
+        every { itemInfo.size } returns 100
+        every { layoutInfo.visibleItemsInfo } returns listOf(itemInfo)
+        every { listState.layoutInfo } returns layoutInfo
+
+        return listState
+    }
+
+    @Test
+    fun `initial state has isFollowingBottom true and pendingCount 0`() {
+        val listState = mockk<LazyListState>(relaxed = true)
+        val scope = TestScope(testDispatcher)
+        val controller = ChatScrollController(listState, scope)
+
+        assertTrue(controller.isFollowingBottom)
+        assertEquals(0, controller.pendingCount)
+    }
+
+    @Test
+    fun `new tail while following keeps pendingCount 0 and requests scroll`() =
+        runTest(testDispatcher) {
+            val listState = mockLazyListStateAtBottom()
+            val controller = ChatScrollController(listState, this)
+
+            controller.onTailChanged(tailKey = "msg-1", messageCount = 1)
+            advanceUntilIdle()
+
+            assertTrue(controller.isFollowingBottom)
+            assertEquals(0, controller.pendingCount)
+            coVerify(atLeast = 1) { listState.scrollToItem(4, any()) }
+        }
+
+    @Test
+    fun `pauseFollowing followed by new messages increments pendingCount`() {
+        val listState = mockk<LazyListState>(relaxed = true)
+        val scope = TestScope(testDispatcher)
+        val controller = ChatScrollController(listState, scope)
+
+        controller.pauseFollowing()
+        assertFalse(controller.isFollowingBottom)
+
+        controller.onTailChanged(tailKey = "msg-1", messageCount = 1)
+        assertEquals(1, controller.pendingCount)
+
+        controller.onTailChanged(tailKey = "msg-2", messageCount = 3)
+        assertEquals(3, controller.pendingCount)
+        assertFalse(controller.isFollowingBottom)
+    }
+
+    @Test
+    fun `resumeFollowing clears pendingCount and restores isFollowingBottom`() =
+        runTest(testDispatcher) {
+            val listState = mockLazyListStateAtBottom()
+            val controller = ChatScrollController(listState, this)
+
+            controller.pauseFollowing()
+            controller.onTailChanged(tailKey = "msg-1", messageCount = 2)
+            assertEquals(2, controller.pendingCount)
+            assertFalse(controller.isFollowingBottom)
+
+            controller.resumeFollowing()
+            advanceUntilIdle()
+
+            assertTrue(controller.isFollowingBottom)
+            assertEquals(0, controller.pendingCount)
+            coVerify(atLeast = 1) { listState.animateScrollToItem(4, any()) }
+        }
+
+    @Test
+    fun `jumpToBottom clears pendingCount and restores isFollowingBottom`() =
+        runTest(testDispatcher) {
+            val listState = mockLazyListStateAtBottom()
+            val controller = ChatScrollController(listState, this)
+
+            controller.pauseFollowing()
+            controller.onTailChanged(tailKey = "msg-1", messageCount = 4)
+            assertEquals(4, controller.pendingCount)
+            assertFalse(controller.isFollowingBottom)
+
+            controller.jumpToBottom(animated = false)
+            advanceUntilIdle()
+
+            assertTrue(controller.isFollowingBottom)
+            assertEquals(0, controller.pendingCount)
+            coVerify(atLeast = 1) { listState.scrollToItem(4, any()) }
+        }
+
+    @Test
+    fun `tail key unchanged causes no change to pendingCount or scroll`() =
+        runTest(testDispatcher) {
+            val listState = mockLazyListStateAtBottom()
+            val controller = ChatScrollController(listState, this)
+
+            controller.pauseFollowing()
+            controller.onTailChanged(tailKey = "same-key", messageCount = 1)
+            assertEquals(1, controller.pendingCount)
+
+            // Repeating the same tailKey should be a no-op
+            controller.onTailChanged(tailKey = "same-key", messageCount = 5)
+            assertEquals(1, controller.pendingCount)
+
+            advanceUntilIdle()
+            coVerify(exactly = 0) { listState.scrollToItem(any(), any()) }
+            coVerify(exactly = 0) { listState.animateScrollToItem(any(), any()) }
+        }
+
+    @Test
+    fun `showFab returns true only when paused and content is present`() {
+        val listState = mockk<LazyListState>(relaxed = true)
+        val scope = TestScope(testDispatcher)
+        val controller = ChatScrollController(listState, scope)
+
+        // Following bottom -> false regardless of contentPresent
+        assertFalse(controller.showFab(contentPresent = true))
+        assertFalse(controller.showFab(contentPresent = false))
+
+        controller.pauseFollowing()
+        // Paused -> true only if contentPresent
+        assertTrue(controller.showFab(contentPresent = true))
+        assertFalse(controller.showFab(contentPresent = false))
+    }
+}