Espresso UI Tests

Espresso Fundamentals

Espresso is Android's standard UI testing framework. It runs on a device or emulator, interacts with real views, and waits for the UI to idle before performing actions.

Basic Structure

@RunWith(AndroidJUnit4::class)
class LoginActivityTest {

    @get:Rule
    val activityRule = ActivityScenarioRule(LoginActivity::class.java)

    @Test
    fun loginWithValidCredentials_navigatesToHome() {
        // Type into email field
        onView(withId(R.id.email_input))
            .perform(typeText("test@example.com"))

        // Type into password field
        onView(withId(R.id.password_input))
            .perform(typeText("password123"))

        // Click login button
        onView(withId(R.id.login_button))
            .perform(click())

        // Verify home screen appears
        onView(withId(R.id.home_welcome_text))
            .check(matches(isDisplayed()))
    }
}

The Three Pillars

1. ViewMatchers — Find views by ID, text, content description, or position.
2. ViewActions — Perform interactions: click, type, scroll, swipe.
3. ViewAssertions — Verify view state: displayed, enabled, text content.

ActivityScenarioRule

ActivityScenarioRule launches the activity before each test and closes it after. It replaces the deprecated ActivityTestRule.

@get:Rule
val activityRule = ActivityScenarioRule(DetailActivity::class.java)

You can pass an Intent to launch with specific extras:

val intent = Intent(ApplicationProvider.getApplicationContext(), DetailActivity::class.java).apply {
    putExtra("product_id", "42")
}
@get:Rule
val activityRule = ActivityScenarioRule(intent)

Espresso Idling Resources

Espresso waits for the UI thread to be idle before performing actions. For background work (network calls, database writes), you must register an idling resource:

@Before
fun setUp() {
    Espresso.registerIdlingResources(countingIdlingResource)
}

@After
fun tearDown() {
    Espresso.unregisterIdlingResources(countingIdlingResource)
}

Without this, Espresso may time out or interact with a partially loaded screen.

Matchers

Matchers find views on screen. Espresso provides several built-in matchers:

// By resource ID
onView(withId(R.id.submit_button))

// By text
onView(withText("Submit"))

// By partial text
onView(withSubstring("Submit"))

// By content description (accessibility)
onView(withContentDescription("Submit button"))

// By view type
onView(isAssignableFrom(EditText::class.java))

// Compound matcher
onView(allOf(
    withId(R.id.button),
    withText("OK"),
    isDisplayed()
))

// Either matcher
onView(anyOf(
    withText("OK"),
    withText("Accept")
))

RecyclerView Matchers

RecyclerView requires special handling because items are not all present at once:

// Scroll to a position
onView(withId(R.id.recycler_view))
    .perform(scrollToPosition<ViewHolder>(5))

// Scroll to a view with specific text
onView(withId(R.id.recycler_view))
    .perform(scrollTo<ViewHolder>(hasDescendant(withText("Target Item"))))

// Click an item at position
onView(withId(R.id.recycler_view))
    .perform(actionOnItemAtPosition<ViewHolder>(0, click()))

// Click item matching a view matcher
onView(withId(R.id.recycler_view))
    .perform(actionOnHolderItem(
        hasDescendant(withText("Target")),
        click()
    ))

Actions

Actions interact with views:

// Click
onView(withId(R.id.button)).perform(click())

// Long click
onView(withId(R.id.button)).perform(longClick())

// Type text (replaces existing text)
onView(withId(R.id.input)).perform(typeText("hello"))

// Type text appended
onView(withId(R.id.input)).perform(replaceText("hello"))

// Clear and type
onView(withId(R.id.input)).perform(clearText(), typeText("hello"))

// Scroll
onView(withId(R.id.scroll_view)).perform(swipeUp())

// Close soft keyboard
onView(withId(R.id.input)).perform(closeSoftKeyboard())

// Press back
onView(withId(R.id.button)).perform(pressBack())

// Custom action
fun clickChildView(id: Int): ViewAction = object : ViewAction {
    override fun getConstraints() = isAssignableFrom(View::class.java)
    override fun getDescription() = "Click child view with id $id"
    override fun perform(uiController: UiController, view: View) {
        view.findViewById<View>(id).performClick()
    }
}

ViewAssertions

Assertions verify view state:

// View is displayed
onView(withId(R.id.text)).check(matches(isDisplayed()))

// View is not displayed
onView(withId(R.id.text)).check(matches(not(isDisplayed())))

// View has specific text
onView(withId(R.id.text)).check(matches(withText("Hello")))

// View has specific error
onView(withId(R.id.input)).check(matches(hasErrorText("Required")))

// View is enabled/disabled
onView(withId(R.id.button)).check(matches(isEnabled()))

// View is checked (for CheckBox, Switch)
onView(withId(R.id.checkbox)).check(matches(isChecked()))

// Count items in RecyclerView
onView(withId(R.id.recycler_view))
    .check(matches(hasChildCount(10)))

Custom Matchers

Write reusable matchers:

fun withDrawable(@DrawableRes id: Int): Matcher<View> {
    return object : BoundedMatcher<View, ImageView>(ImageView::class.java) {
        override fun describeTo(description: Description) {
            description.appendText("with drawable id $id")
        }

        override fun matchesSafely(imageView: ImageView): Boolean {
            val drawable = ContextCompat.getDrawable(imageView.context, id)
            return imageView.drawable?.constantState == drawable?.constantState
        }
    }
}