Testing a Composable with assertTextEquals() fails with IllegalStateException

Question

I am testing a simple TextField composable and I am using onNodeWithContentDescription() to locate this TextField which I have applied semantics on its modifier.

TextField(
                modifier = Modifier
                        .fillMaxWidth()
                        .semantics { contentDescription = "TextField" },
                value = text,
                onValueChange = { onTextChange(it) },

This is my test function:

@get:Rule
    val composeTestRule = createComposeRule()

    @Test
    fun openSearchWidget_enterInputText_assertInputText() {
        var text by mutableStateOf("")
        
        composeTestRule.setContent {
         

            SearchWidget(text = text, onTextChange = { text = it }))

            
            composeTestRule.onNodeWithContentDescription("TextField")
                    .performTextInput("Tonnie")

            composeTestRule.onNodeWithContentDescription("TextField")
                    .assertTextEquals("Tonnie")
        }
}

The Test is failing with this error.

java.lang.IllegalStateException: Functions that involve synchronization (Assertions, Actions, Synchronization; e.g. assertIsSelected(), doClick(), runOnIdle()) cannot be run from the main thread. Did you nest such a function inside runOnIdle {}, runOnUiThread {} or setContent {}? at androidx.compose.ui.test.junit4.EspressoLink.runUntilIdle(EspressoLink.android.kt:73) at androidx.compose.ui.test.AndroidComposeUiTestEnvironment.waitForIdle(ComposeUiTest.android.kt:308) at androidx.compose.ui.test.AndroidComposeUiTestEnvironment.access$waitForIdle(ComposeUiTest.android.kt:217)

I have already wrapped my test function with setContent{} but still the text fails.

Please help me to resolve this.

Answer 1

Assertions cannot be run in main thread. The entire main thread is inside setContent. Put this outside the scope of setContent and it should work:

        composeTestRule.onNodeWithContentDescription("TextField")
                .performTextInput("Tonnie")

        composeTestRule.onNodeWithContentDescription("TextField")
                .assertTextEquals("Tonnie")