Compose UI testing in Android Kotlin - Mini App: Build & Ship

Build: Greeting Screen

A simple screen that shows a greeting message and a button to change the greeting.

Target UI

---------------------
| Greeting Screen    |
|-------------------|
| Hello, User!       |
|                   |
| [Change Greeting]  |
---------------------

Display a Text composable with initial text 'Hello, User!'

Display a Button below the text labeled 'Change Greeting'

When the button is clicked, the text changes to 'Welcome to Compose UI Testing!'

Write a Compose UI test to verify the initial text is shown

Write a Compose UI test to verify the text changes after button click

Starter Code

Android Kotlin

import androidx.compose.foundation.layout.Column
import androidx.compose.material3.Button
import androidx.compose.material3.Text
import androidx.compose.runtime.*
import androidx.compose.ui.Modifier

@Composable
fun GreetingScreen() {
    // TODO: Add state and UI here
}

Task 1

Task 2

Task 3

Solution

Android Kotlin

import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.padding
import androidx.compose.material3.Button
import androidx.compose.material3.Text
import androidx.compose.runtime.*
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.testTag
import androidx.compose.ui.unit.dp

@Composable
fun GreetingScreen() {
    var greeting by remember { mutableStateOf("Hello, User!") }

    Column(modifier = Modifier.padding(16.dp)) {
        Text(
            text = greeting,
            modifier = Modifier.testTag("greetingText")
        )
        Button(
            onClick = { greeting = "Welcome to Compose UI Testing!" },
            modifier = Modifier.testTag("changeGreetingButton")
        ) {
            Text("Change Greeting")
        }
    }
}

We use remember and mutableStateOf to hold the greeting text state. The Text composable shows the current greeting. The Button updates the greeting when clicked. We add testTag modifiers to identify UI elements in tests easily.

Final Result

Completed Screen

---------------------
| Greeting Screen    |
|-------------------|
| Hello, User!       |
|                   |
| [Change Greeting]  |
---------------------

User sees 'Hello, User!' text initially

User taps 'Change Greeting' button

Text changes to 'Welcome to Compose UI Testing!'

Stretch Goal

Write a Compose UI test that clicks the button and verifies the text changes

💡 Hint

Use createComposeRule(), onNodeWithTag(), performClick(), and assertTextEquals()

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