Compose UI testing in Android Kotlin

Introduction

Compose UI testing helps you check if your app's screen looks and works right. It makes sure buttons, texts, and other parts behave as expected.

You want to check if a button click changes the screen correctly.

You want to verify that a text label shows the right message.

You want to test if a list displays the correct items.

You want to make sure your UI works well after changes.

You want to catch bugs before users see them.

Syntax

Android Kotlin

createComposeRule().apply {
  onNodeWithText("Button Text").performClick()
  onNodeWithText("Result Text").assertIsDisplayed()
}

createComposeRule() sets up the test environment for Compose UI.

onNodeWithText() finds UI elements by their visible text.

Examples

Clicks a button or element with text "Click Me".

Android Kotlin

composeTestRule.onNodeWithText("Click Me").performClick()

Checks if the text "Hello World" is visible on the screen.

Android Kotlin

composeTestRule.onNodeWithText("Hello World").assertIsDisplayed()

Finds a UI element by a test tag and checks it exists.

Android Kotlin

composeTestRule.onNodeWithTag("myButton").assertExists()

Sample App

This test shows a button labeled "Say Hello". When clicked, it shows the text "Hello!". The test clicks the button and checks if the greeting text appears.

Android Kotlin

import androidx.compose.material3.*
import androidx.compose.runtime.Composable
import androidx.compose.ui.test.junit4.createComposeRule
import androidx.compose.ui.test.*
import org.junit.Rule
import org.junit.Test

class MyComposeTest {
  @get:Rule
  val composeTestRule = createComposeRule()

  @Composable
  fun GreetingButton() {
    var clicked = false
    Button(onClick = { clicked = true }) {
      Text("Say Hello")
    }
    if (clicked) {
      Text("Hello!")
    }
  }

  @Test
  fun testGreetingButton() {
    composeTestRule.setContent {
      GreetingButton()
    }
    composeTestRule.onNodeWithText("Say Hello").assertIsDisplayed()
    composeTestRule.onNodeWithText("Say Hello").performClick()
    composeTestRule.onNodeWithText("Hello!").assertIsDisplayed()
  }
}

Important Notes

Use onNodeWithText to find elements by visible text.

Use performClick() to simulate user taps.

Use assertIsDisplayed() to check if UI elements are visible.

Summary

Compose UI testing helps check your app's screens work as expected.

Use createComposeRule() to set up tests.

Find UI elements by text or tags, then perform actions or checks.

Practice

1. What is the main purpose of createComposeRule() in Compose UI testing?

easy

A. To create UI elements dynamically during runtime

B. To set up the environment for testing Compose UI components

C. To launch the app on a physical device

D. To generate random test data for UI tests

Solution

1. Step 1: Understand the role of createComposeRule()

   This function sets up the Compose testing environment so you can test UI components safely and isolated.

2. Step 2: Differentiate from other options

   It does not create UI elements dynamically, launch apps, or generate test data; it only prepares the test rule.

3. Final Answer:

   To set up the environment for testing Compose UI components -> Option B

4. Quick Check:

   Compose test setup = B [OK]

Hint: Remember: createComposeRule sets up Compose test environment [OK]

Common Mistakes:

• Thinking it creates UI elements during app runtime
• Confusing it with launching the app on devices
• Assuming it generates test data automatically

2. Which of the following is the correct way to find a UI element by its text in Compose UI testing?

easy

A. composeTestRule.getElementByText("Hello")

B. composeTestRule.findViewByText("Hello")

C. composeTestRule.selectNode("Hello")

D. composeTestRule.onNodeWithText("Hello")

Solution

1. Step 1: Recall Compose testing API for text search

   The correct method to find a node by text is onNodeWithText().

2. Step 2: Verify other options are invalid

   Methods like findViewByText, getElementByText, and selectNode do not exist in Compose testing.

3. Final Answer:

   composeTestRule.onNodeWithText("Hello") -> Option D

4. Quick Check:

   Find by text = onNodeWithText [OK]

Hint: Use onNodeWithText to find text elements in Compose tests [OK]

Common Mistakes:

• Using Android View testing methods instead of Compose methods
• Trying to use non-existent functions
• Confusing node selectors with view selectors

3. Given this Compose test code snippet:

composeTestRule.setContent {
  Text("Welcome")
}

composeTestRule.onNodeWithText("Welcome").assertExists()

What will happen when this test runs?

medium

A. The test will pass because the text "Welcome" exists

B. The test will fail because the text is not found

C. The test will throw a syntax error

D. The test will pass but not check the text

Solution

1. Step 1: Analyze the UI content set

   The UI contains a Text composable with the string "Welcome".

2. Step 2: Understand the assertion

   assertExists() checks that the node with text "Welcome" is present, which it is.

3. Final Answer:

   The test will pass because the text "Welcome" exists -> Option A

4. Quick Check:

   Text present means assertExists passes [OK]

Hint: assertExists passes if UI text is present exactly [OK]

Common Mistakes:

• Assuming assertExists checks content correctness beyond presence
• Thinking the test fails if no interaction is done
• Confusing syntax errors with runtime test failures

4. Identify the error in this Compose UI test code:

composeTestRule.setContent {
  Button(onClick = {}) {
    Text("Click Me")
  }
}

composeTestRule.onNodeWithTag("button").performClick()

medium

A. performClick() is not a valid Compose test function

B. The Button composable cannot be clicked in tests

C. The node is searched by tag but no tag was set on the Button

D. The Text inside Button should be searched instead of Button

Solution

1. Step 1: Check how the node is found

   The test looks for a node with tag "button" but the Button has no tag set.

2. Step 2: Understand Compose testing tags

   To find by tag, the Button must have Modifier.testTag("button") applied, which is missing.

3. Final Answer:

   The node is searched by tag but no tag was set on the Button -> Option C

4. Quick Check:

   Missing testTag causes node not found [OK]

Hint: Always add testTag modifier to find nodes by tag [OK]

Common Mistakes:

• Assuming performClick works without correct node selection
• Searching text inside Button instead of Button itself
• Thinking performClick is invalid in Compose tests

5. You want to test a Compose screen with a list of items. Each item has a unique test tag like "item_1", "item_2", etc. Which approach correctly verifies that the item with tag "item_3" is displayed and clickable?

hard

A. composeTestRule.onNodeWithTag("item_3").assertIsDisplayed().performClick()

B. composeTestRule.onNodeWithText("item_3").assertIsDisplayed().performClick()

C. composeTestRule.onNodeWithTag("item_3").assertExists().performClick()

D. composeTestRule.onNodeWithContentDescription("item_3").assertIsDisplayed().performClick()

Solution

1. Step 1: Identify correct node selector for test tag

   Use onNodeWithTag("item_3") to find the node by its unique test tag.

2. Step 2: Verify visibility and interaction

   assertIsDisplayed() confirms the node is visible, and performClick() simulates a click.

3. Step 3: Eliminate incorrect options

   Searching by text or content description is wrong here; assertExists() alone doesn't check visibility.

4. Final Answer:

   composeTestRule.onNodeWithTag("item_3").assertIsDisplayed().performClick() -> Option A

5. Quick Check:

   Tag + visible + click = composeTestRule.onNodeWithTag("item_3").assertIsDisplayed().performClick() [OK]

Hint: Use onNodeWithTag + assertIsDisplayed before performClick [OK]

Common Mistakes:

• Using onNodeWithText instead of onNodeWithTag for tags
• Skipping assertIsDisplayed before clicking
• Confusing content description with test tag