Add Android testing skill for Claude (#6370)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

.claude/skills/testing-android-code/references/flow-testing-patterns.md

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+# Flow Testing with Turbine
+
+Bitwarden Android uses Turbine for testing Kotlin Flows, including the critical distinction between StateFlow and EventFlow patterns.
+
+## StateFlow vs EventFlow
+
+### StateFlow (Replayed)
+
+**Characteristics:**
+- `replay = 1` - Always emits current value to new collectors
+- First `awaitItem()` returns the current/initial state
+- Survives configuration changes
+- Used for UI state that needs to be immediately available
+
+**Test Pattern:**
+```kotlin
+@Test
+fun `action should update state`() = runTest {
+    val viewModel = MyViewModel(savedStateHandle, mockRepository)
+
+    viewModel.stateFlow.test {
+        // First awaitItem() gets CURRENT state
+        assertEquals(INITIAL_STATE, awaitItem())
+
+        // Trigger action
+        viewModel.trySendAction(MyAction.LoadData)
+
+        // Next awaitItem() gets UPDATED state
+        assertEquals(LOADING_STATE, awaitItem())
+        assertEquals(SUCCESS_STATE, awaitItem())
+    }
+}
+```
+
+### EventFlow (No Replay)
+
+**Characteristics:**
+- `replay = 0` - Only emits new events after subscription
+- No initial value emission
+- One-time events (navigation, toasts, dialogs)
+- Does not survive configuration changes
+
+**Test Pattern:**
+```kotlin
+@Test
+fun `action should emit event`() = runTest {
+    val viewModel = MyViewModel(savedStateHandle, mockRepository)
+
+    viewModel.eventFlow.test {
+        // MUST call expectNoEvents() first - nothing emitted yet
+        expectNoEvents()
+
+        // Trigger action
+        viewModel.trySendAction(MyAction.Submit)
+
+        // Now expect the event
+        assertEquals(MyEvent.NavigateToNext, awaitItem())
+    }
+}
+```
+
+**Critical:** Always call `expectNoEvents()` before triggering actions on EventFlow. Forgetting this causes flaky tests.
+
+## Testing State and Events Simultaneously
+
+Use the `stateEventFlow()` helper from `BaseViewModelTest`:
+
+```kotlin
+@Test
+fun `complex action should update state and emit event`() = runTest {
+    val viewModel = MyViewModel(savedStateHandle, mockRepository)
+
+    viewModel.stateEventFlow(backgroundScope) { stateFlow, eventFlow ->
+        // Initial state
+        assertEquals(INITIAL_STATE, stateFlow.awaitItem())
+
+        // No events yet
+        eventFlow.expectNoEvents()
+
+        // Trigger action
+        viewModel.trySendAction(MyAction.ComplexAction)
+
+        // Verify state progression
+        assertEquals(LOADING_STATE, stateFlow.awaitItem())
+        assertEquals(SUCCESS_STATE, stateFlow.awaitItem())
+
+        // Verify event emission
+        assertEquals(MyEvent.ShowToast, eventFlow.awaitItem())
+    }
+}
+```
+
+## Repository Flow Testing
+
+### Testing Database Flows
+
+```kotlin
+@Test
+fun `dataFlow should emit when database updates`() = runTest {
+    val dataFlow = MutableStateFlow(initialData)
+    every { mockDiskSource.dataFlow } returns dataFlow
+
+    repository.dataFlow.test {
+        // Initial value
+        assertEquals(initialData, awaitItem())
+
+        // Update disk source
+        dataFlow.value = updatedData
+
+        // Verify emission
+        assertEquals(updatedData, awaitItem())
+    }
+}
+```
+
+### Testing Transformed Flows
+
+```kotlin
+@Test
+fun `flow transformation should map correctly`() = runTest {
+    val sourceFlow = MutableStateFlow(UserEntity(id = "1", name = "John"))
+    every { mockDao.observeUser() } returns sourceFlow
+
+    // Repository transforms entity to domain model
+    repository.userFlow.test {
+        val expectedUser = User(id = "1", name = "John")
+        assertEquals(expectedUser, awaitItem())
+    }
+}
+```
+
+## Common Patterns
+
+### Pattern 1: Testing Initial State + Action
+
+```kotlin
+@Test
+fun `load data should update from idle to loading to success`() = runTest {
+    coEvery { repository.getData() } returns "data".asSuccess()
+
+    viewModel.stateFlow.test {
+        assertEquals(DEFAULT_STATE, awaitItem())
+
+        viewModel.loadData()
+
+        assertEquals(DEFAULT_STATE.copy(loadingState = LoadingState.Loading), awaitItem())
+        assertEquals(DEFAULT_STATE.copy(loadingState = LoadingState.Success), awaitItem())
+    }
+}
+```
+
+### Pattern 2: Testing Error States
+
+```kotlin
+@Test
+fun `load data with error should emit failure state`() = runTest {
+    val error = Exception("Network error")
+    coEvery { repository.getData() } returns error.asFailure()
+
+    viewModel.stateFlow.test {
+        assertEquals(DEFAULT_STATE, awaitItem())
+
+        viewModel.loadData()
+
+        assertEquals(DEFAULT_STATE.copy(loadingState = LoadingState.Loading), awaitItem())
+        assertEquals(
+            DEFAULT_STATE.copy(loadingState = LoadingState.Error("Network error")),
+            awaitItem(),
+        )
+    }
+}
+```
+
+### Pattern 3: Testing Event Sequences
+
+```kotlin
+@Test
+fun `submit should emit validation then navigation events`() = runTest {
+    viewModel.eventFlow.test {
+        expectNoEvents()
+
+        viewModel.trySendAction(MyAction.Submit)
+
+        assertEquals(MyEvent.ShowValidation, awaitItem())
+        assertEquals(MyEvent.NavigateToNext, awaitItem())
+    }
+}
+```
+
+### Pattern 4: Testing Cancellation
+
+```kotlin
+@Test
+fun `cancelling collection should stop emissions`() = runTest {
+    val flow = flow {
+        repeat(100) {
+            emit(it)
+            delay(100)
+        }
+    }
+
+    flow.test {
+        assertEquals(0, awaitItem())
+        assertEquals(1, awaitItem())
+
+        // Cancel after 2 items
+        cancel()
+
+        // No more items received
+    }
+}
+```
+
+## Anti-Patterns
+
+### ❌ Forgetting expectNoEvents() on EventFlow
+
+```kotlin
+// WRONG
+viewModel.eventFlow.test {
+    viewModel.trySendAction(action)  // May fail - no initial expectNoEvents
+    assertEquals(event, awaitItem())
+}
+
+// CORRECT
+viewModel.eventFlow.test {
+    expectNoEvents()  // ALWAYS do this first
+    viewModel.trySendAction(action)
+    assertEquals(event, awaitItem())
+}
+```
+
+### ❌ Not Using runTest
+
+```kotlin
+// WRONG - Missing runTest
+@Test
+fun `test flow`() {
+    flow.test { /* ... */ }
+}
+
+// CORRECT
+@Test
+fun `test flow`() = runTest {
+    flow.test { /* ... */ }
+}
+```
+
+### ❌ Mixing StateFlow and EventFlow Patterns
+
+```kotlin
+// WRONG - Treating StateFlow like EventFlow
+stateFlow.test {
+    expectNoEvents()  // Unnecessary - StateFlow always has value
+    /* ... */
+}
+
+// WRONG - Treating EventFlow like StateFlow
+eventFlow.test {
+    val item = awaitItem()  // Will hang - no initial value!
+    /* ... */
+}
+```
+
+## Reference Implementations
+
+**ViewModel with StateFlow and EventFlow:**
+`app/src/test/kotlin/com/x8bit/bitwarden/ui/tools/feature/generator/GeneratorViewModelTest.kt`
+
+**Repository Flow Testing:**
+`data/src/test/kotlin/com/bitwarden/data/tools/generator/repository/GeneratorRepositoryTest.kt`
+
+**Complex Flow Transformations:**
+`data/src/test/kotlin/com/bitwarden/data/vault/repository/VaultRepositoryTest.kt`