Compose Testing Advanced 01: runOnIdle and waitForIdle ⏳

Introduction

Welcome to the first installment of our advanced series on Compose Testing! In this post, we’ll dive into the concepts of runOnIdle and waitForIdle. These tools are essential for managing asynchronous tasks and ensuring that your UI tests run smoothly without flakiness. By mastering these techniques, you can improve the reliability and stability of your Compose tests.

Understanding Idle States in Compose Testing

In Compose testing, handling idle states is crucial for ensuring that your UI is fully rendered and all asynchronous operations are completed before performing assertions or interactions. The ComposeTestRule provides utility functions like runOnIdle and waitForIdle to help manage these states.

runOnIdle 🕰️

The runOnIdle function allows you to run a block of code when the Compose framework is idle. This is useful for performing assertions or actions after all pending tasks are completed.

Example: Using runOnIdle

Let’s create a simple example where we need to verify the state of a UI element after an asynchronous operation.

@Test
fun testRunOnIdle() {
    composeTestRule.setContent {
        var text by remember { mutableStateOf("Initial Text") }
        
        // Simulating an asynchronous operation
        LaunchedEffect(Unit) {
            delay(1000)
            text = "Updated Text"
        }
        
        Text(text)
    }
    
    // Perform an assertion when the UI is idle
    composeTestRule.runOnIdle {
        composeTestRule.onNodeWithText("Updated Text").assertExists()
    }
}

In this example:

1. We set up a simple UI with a Text composable whose content is updated asynchronously after a delay.
2. We use LaunchedEffect to simulate the asynchronous update.
3. We use runOnIdle to assert that the text has been updated once the Compose framework is idle.

waitForIdle ⌛

The waitForIdle function blocks the test execution until the Compose framework is idle. This is useful when you need to ensure that all pending tasks are completed before proceeding with the next steps in your test.

Example: Using waitForIdle

Let’s enhance the previous example by using waitForIdle to ensure that the UI is fully rendered before performing our assertions.

@Test
fun testWaitForIdle() {
    composeTestRule.setContent {
        var text by remember { mutableStateOf("Initial Text") }
        
        // Simulating an asynchronous operation
        LaunchedEffect(Unit) {
            delay(1000)
            text = "Updated Text"
        }
        
        Text(text)
    }
    
    // Wait for the UI to be idle
    composeTestRule.waitForIdle()
    
    // Perform the assertion
    composeTestRule.onNodeWithText("Updated Text").assertExists()
}

In this example:

1. The setup is similar to the previous one, with an asynchronous update to a Text composable.
2. We use waitForIdle to block the test execution until the UI is idle.
3. Once the UI is idle, we assert that the text has been updated.

Combining runOnIdle and waitForIdle 🔄

You can combine runOnIdle and waitForIdle to handle more complex scenarios where you need to perform actions or assertions based on the UI's idle state.

Example: Combining runOnIdle and waitForIdle

Consider a scenario where you need to perform an action after the UI is idle and then wait for another idle state before performing assertions.

@Test
fun testCombinedIdleHandling() {
    composeTestRule.setContent {
        var text by remember { mutableStateOf("Initial Text") }
        
        // Simulating an asynchronous operation
        LaunchedEffect(Unit) {
            delay(1000)
            text = "Updated Text"
        }
        
        Text(text)
    }
    
    // Wait for the initial idle state
    composeTestRule.waitForIdle()
    
    // Perform an action when the UI is idle
    composeTestRule.runOnIdle {
        // Simulate another UI update
        composeTestRule.setContent {
            var text by remember { mutableStateOf("Initial Text") }
            
            LaunchedEffect(Unit) {
                delay(500)
                text = "Final Text"
            }
            
            Text(text)
        }
    }
    
    // Wait for the final idle state
    composeTestRule.waitForIdle()
    
    // Perform the final assertion
    composeTestRule.onNodeWithText("Final Text").assertExists()
}

In this example:

1. We set up a UI with an initial asynchronous update.
2. We wait for the initial idle state using waitForIdle.
3. We use runOnIdle to perform another UI update when the initial idle state is reached.
4. We wait for the final idle state using waitForIdle.
5. We perform the final assertion to verify the UI state.

Best Practices for Using runOnIdle and waitForIdle 💡

1. Avoid Overusing waitForIdle: While waitForIdle is useful, overusing it can lead to slower tests. Use it judiciously to ensure efficient test execution.
2. Combine with Assertions: Use runOnIdle to perform critical assertions that depend on the UI's idle state.
3. Debugging Asynchronous Issues: If your tests are flaky, using these functions can help stabilize them by ensuring that assertions and actions are performed only when the UI is fully rendered and idle.

Next Steps: Custom Matchers and Assertions 🧩

Ready to enhance your Compose testing skills with custom tools? In our next blog, Compose Testing Advanced 02: Custom Matchers and Assertions, we delve into creating and using custom matchers and assertions to simplify complex test conditions and improve test readability. This guide will provide detailed examples and best practices for making your tests more efficient and maintainable.

Read the next blog: Compose Testing Advanced 02: Custom Matchers and Assertions 🧩

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