1. RED    → Write a failing test for desired behavior
2. GREEN  → Write MINIMUM code to make it pass
3. REFACTOR → Clean up while keeping tests green
4. REPEAT → Next behavior

        /  UI  \        10% - Espresso, end-to-end flows
       /--------\
      / Integra- \      20% - ViewModel+Repository, Room, API
     /  tion      \
    /--------------\
   /   Unit Tests   \   70% - Pure Kotlin, fast, isolated
  /==================\

@Test
fun addItemToCart_increasesCartCount() {
    val cart = ShoppingCart()
    cart.addItem(Product("Phone", 999.99))
    assertEquals(1, cart.itemCount)
}

class ShoppingCart {
    private val items = mutableListOf<Product>()
    fun addItem(product: Product) { items.add(product) }
    val itemCount: Int get() = items.size
}

@Test
fun addMultipleItems_calculatesTotal() {
    val cart = ShoppingCart()
    cart.addItem(Product("Phone", 999.99))
    cart.addItem(Product("Case", 29.99))
    assertEquals(1029.98, cart.totalPrice, 0.01)
}

class ScoreTest {
    @Test
    fun increment_increasesCurrentScore() {
        val score = Score()
        score.increment()
        assertEquals(1, score.current)
    }
}

@RunWith(AndroidJUnit4::class)
class WishlistDaoTest {
    private lateinit var db: AppDatabase

    @Before
    fun setup() {
        db = Room.inMemoryDatabaseBuilder(
            ApplicationProvider.getApplicationContext(),
            AppDatabase::class.java
        ).build()
    }

    @After
    fun teardown() { db.close() }
}

class ApiServiceTest {
    private val mockWebServer = MockWebServer()

    @Test
    fun fetchData_returnsExpectedResponse() {
        mockWebServer.enqueue(
            MockResponse().setBody("""{"id":1,"name":"Test"}""").setResponseCode(200)
        )
        val response = service.fetchData().execute()
        assertEquals("Test", response.body()?.name)
    }
}

@Test
fun clickSaveButton_showsConfirmation() {
    onView(withId(R.id.saveButton)).perform(click())
    onView(withText("Saved!")).check(matches(isDisplayed()))
}

dependencies {
    // Unit
    testImplementation 'junit:junit:4.13.2'
    testImplementation 'org.mockito.kotlin:mockito-kotlin:5.2.1'
    testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.7.3'

    // Integration & UI
    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
    androidTestImplementation 'androidx.arch.core:core-testing:2.2.0'

    // Room & Network
    testImplementation 'androidx.room:room-testing:2.6.1'
    testImplementation 'com.squareup.okhttp3:mockwebserver:4.12.0'
}

fun addItem_emptyCart_cartHasOneItem()
fun calculateTotal_multipleItems_returnsSumOfPrices()
fun login_invalidCredentials_returnsError()
fun fetchUsers_networkError_showsErrorState()

feature-planning → Define specs & acceptance criteria
      ↓
android-tdd → Write tests first, then implement (THIS SKILL)
      ↓
android-development → Follow architecture & Kotlin standards
      ↓
ai-error-handling → Validate AI-generated implementations
      ↓
vibe-security-skill → Security review

name: Android TDD
on: [push, pull_request]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Unit Tests
        run: ./gradlew test
      - name: Instrumented Tests
        run: ./gradlew connectedAndroidTest
      - name: Coverage Report
        run: ./gradlew jacocoTestReport