Add Android testing skill for Claude (#6370)

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

.claude/skills/testing-android-code/examples/viewmodel-test-example.md

@@ -0,0 +1,161 @@
+/**
+ * Complete ViewModel Test Example
+ *
+ * Key patterns demonstrated:
+ * - Extending BaseViewModelTest
+ * - Testing StateFlow with Turbine
+ * - Testing EventFlow with Turbine
+ * - Using stateEventFlow() for simultaneous testing
+ * - MockK mocking patterns
+ * - Test factory method design (accepts domain state, not SavedStateHandle)
+ * - Complete state assertions (assert entire state objects)
+ */
+package com.bitwarden.example.feature
+
+import androidx.lifecycle.SavedStateHandle
+import app.cash.turbine.test
+import com.bitwarden.ui.platform.base.BaseViewModelTest
+import io.mockk.coEvery
+import io.mockk.coVerify
+import io.mockk.every
+import io.mockk.mockk
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.test.runTest
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+class ExampleViewModelTest : BaseViewModelTest() {
+
+    // Mock dependencies
+    private val mockRepository: ExampleRepository = mockk()
+    private val mockAuthDiskSource: AuthDiskSource = mockk {
+        every { userStateFlow } returns MutableStateFlow(null)
+    }
+
+    /**
+     * StateFlow has replay=1, so first awaitItem() returns current state
+     */
+    @Test
+    fun `initial state should be default state`() = runTest {
+        val viewModel = createViewModel()
+
+        viewModel.stateFlow.test {
+            assertEquals(DEFAULT_STATE, awaitItem())
+        }
+    }
+
+    /**
+     * Test state transitions: initial -> loading -> success
+     */
+    @Test
+    fun `LoadData action should update state from idle to loading to success`() = runTest {
+        val expectedData = "loaded data"
+        coEvery { mockRepository.fetchData(any()) } returns Result.success(expectedData)
+
+        val viewModel = createViewModel()
+
+        viewModel.stateFlow.test {
+            assertEquals(DEFAULT_STATE, awaitItem())
+
+            viewModel.trySendAction(ExampleAction.LoadData)
+
+            assertEquals(DEFAULT_STATE.copy(isLoading = true), awaitItem())
+            assertEquals(DEFAULT_STATE.copy(isLoading = false, data = expectedData), awaitItem())
+        }
+
+        coVerify { mockRepository.fetchData(any()) }
+    }
+
+    /**
+     * EventFlow has no replay - MUST call expectNoEvents() first
+     */
+    @Test
+    fun `SubmitClick action should emit NavigateToNext event`() = runTest {
+        coEvery { mockRepository.submitData(any()) } returns Result.success(Unit)
+
+        val viewModel = createViewModel()
+
+        viewModel.eventFlow.test {
+            expectNoEvents() // CRITICAL for EventFlow
+            viewModel.trySendAction(ExampleAction.SubmitClick)
+            assertEquals(ExampleEvent.NavigateToNext, awaitItem())
+        }
+    }
+
+    /**
+     * Use stateEventFlow() helper for simultaneous testing
+     */
+    @Test
+    fun `complex action should update state and emit event`() = runTest {
+        coEvery { mockRepository.complexOperation(any()) } returns Result.success("result")
+
+        val viewModel = createViewModel()
+
+        viewModel.stateEventFlow(backgroundScope) { stateFlow, eventFlow ->
+            assertEquals(DEFAULT_STATE, stateFlow.awaitItem())
+            eventFlow.expectNoEvents()
+
+            viewModel.trySendAction(ExampleAction.ComplexAction)
+
+            assertEquals(DEFAULT_STATE.copy(isLoading = true), stateFlow.awaitItem())
+            assertEquals(DEFAULT_STATE.copy(data = "result"), stateFlow.awaitItem())
+            assertEquals(ExampleEvent.ShowToast("Success!"), eventFlow.awaitItem())
+        }
+    }
+
+    /**
+     * Test state restoration from saved state.
+     * Note: Use initialState parameter, NOT SavedStateHandle directly.
+     */
+    @Test
+    fun `initial state from saved state should be preserved`() = runTest {
+        // Build complete expected state - always assert full objects
+        val savedState = ExampleState(
+            isLoading = false,
+            data = "restored data",
+            errorMessage = null,
+        )
+
+        val viewModel = createViewModel(initialState = savedState)
+
+        viewModel.stateFlow.test {
+            assertEquals(savedState, awaitItem())
+        }
+    }
+
+    /**
+     * Factory method accepts domain state, NOT SavedStateHandle.
+     * This hides Android framework details from test logic.
+     */
+    private fun createViewModel(
+        initialState: ExampleState? = null,
+    ): ExampleViewModel = ExampleViewModel(
+        savedStateHandle = SavedStateHandle().apply { set("state", initialState) },
+        repository = mockRepository,
+        authDiskSource = mockAuthDiskSource,
+    )
+}
+
+private val DEFAULT_STATE = ExampleState(
+    isLoading = false,
+    data = null,
+    errorMessage = null,
+)
+
+// Example types (normally in separate files)
+data class ExampleState(
+    val isLoading: Boolean = false,
+    val data: String? = null,
+    val errorMessage: String? = null,
+)
+
+sealed class ExampleAction {
+    data object LoadData : ExampleAction()
+    data object SubmitClick : ExampleAction()
+    data object ComplexAction : ExampleAction()
+}
+
+sealed class ExampleEvent {
+    data object NavigateToNext : ExampleEvent()
+    data class ShowToast(val message: String) : ExampleEvent()
+}