@Test
fun greeterSaysHello() {
    onView(withId(R.id.name_field)).perform(typeText("Steve"))
    onView(withId(R.id.greet_button)).perform(click())
    onView(withText("Hello Steve!")).check(matches(isDisplayed()))
}

// app/build.gradle
android {
    defaultConfig {
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
}

dependencies {
    androidTestImplementation 'androidx.test.ext:junit:1.2.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.6.1'
    androidTestImplementation 'androidx.test.espresso:espresso-contrib:3.6.1'
    androidTestImplementation 'androidx.test.espresso:espresso-intents:3.6.1'
    androidTestImplementation 'androidx.test:rules:1.6.1'
}

import androidx.test.espresso.Espresso.onView
import androidx.test.espresso.action.ViewActions.*
import androidx.test.espresso.assertion.ViewAssertions.*
import androidx.test.espresso.matcher.ViewMatchers.*
import androidx.test.ext.junit.rules.ActivityScenarioRule

@RunWith(AndroidJUnit4::class)
class CheckoutTest {
    @get:Rule
    val activityRule = ActivityScenarioRule(MainActivity::class.java)

    @Test
    fun applyPromoCode() {
        onView(withId(R.id.promo_field)).perform(typeText("WELCOME10"), closeSoftKeyboard())
        onView(withId(R.id.apply_button)).perform(click())
        onView(withId(R.id.subtotal)).check(matches(withText("$22.49")))
    }
}

class NetworkIdlingResource : IdlingResource {
    @Volatile private var callback: IdlingResource.ResourceCallback? = null
    @Volatile private var pendingRequests = 0

    override fun getName() = "NetworkIdlingResource"
    override fun isIdleNow() = pendingRequests == 0
    override fun registerIdleTransitionCallback(cb: IdlingResource.ResourceCallback) {
        callback = cb
    }

    fun increment() = synchronized(this) { pendingRequests++ }
    fun decrement() = synchronized(this) {
        pendingRequests--
        if (pendingRequests == 0) callback?.onTransitionToIdle()
    }
}

// Wire from production code at network call sites:
networkIdlingResource.increment()
api.fetchOrders().enqueue { _, _ -> networkIdlingResource.decrement() }

// Register in test setup:
@Before fun setup() { IdlingRegistry.getInstance().register(networkIdlingResource) }
@After  fun teardown() { IdlingRegistry.getInstance().unregister(networkIdlingResource) }

// Matchers
withId(R.id.button)              // by ID
withText("Submit")                // by displayed text
withContentDescription("Login")   // by content description
hasSibling(withText("Email"))     // structural relationship
isDisplayed()                     // currently visible

// Actions
click(), longClick()
typeText("..."), clearText()
scrollTo(), swipeLeft(), swipeUp()
pressBack()

// Assertions
matches(withText("Hello"))
matches(isDisplayed())
matches(isEnabled())
doesNotExist()

// espresso-contrib provides RecyclerViewActions
onView(withId(R.id.cart_list))
    .perform(RecyclerViewActions.actionOnItemAtPosition<MyViewHolder>(0, click()))

onView(withId(R.id.cart_list))
    .perform(RecyclerViewActions.scrollTo<MyViewHolder>(hasDescendant(withText("BOOK-001"))))

# Unit + UI tests on connected device / emulator
./gradlew connectedAndroidTest

# With test orchestrator (each test in fresh process - preferred for isolation):
android {
    defaultConfig {
        testInstrumentationRunnerArguments clearPackageData: 'true'
    }
    testOptions {
        execution 'ANDROIDX_TEST_ORCHESTRATOR'
    }
}

jobs:
  ui-tests:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v5
      - uses: reactivecircus/android-emulator-runner@v2
        with:
          api-level: 34
          script: ./gradlew connectedAndroidTest
      - uses: actions/upload-artifact@v4
        if: always()
        with:
          name: test-results
          path: app/build/outputs/androidTest-results