Test A2UI components and surfaces

The androidx.a2ui.compose:compose-ui-testing testing library provides testing APIs that use a controller pattern idiomatic to Jetpack testing libraries, such as Navigation's TestNavHostController.

Unlike standard Jetpack Compose components that take static parameters and emit UI, A2UI components are contextual. They rely on A2uiComponentScope to evaluate dynamic data bindings, dispatch outbound actions to the agent, write back to two-way data bindings, and inflate dynamic child templates.

The testing APIs simplify test setup while provisioning real A2uiMessageProcessor instances, running their coroutines bound to the Compose test environment.

Isolated components

You can verify that an individual component resolves its data, dispatches actions, and renders correctly within your design system theme:

@Test
fun button_resolvesStubChildAndDispatchesAction() = runComposeUiTest {
    // 1. Create the test controller
    val controller = A2uiTestController(
        // Provide a catalog containing the component under test
        catalog = CustomComponentCatalog,
        // Configure the component under test with concrete properties
        initialComponents = listOf(
            A2uiComponentPayload(
                id = "root",
                type = "Button",
                properties = mapOf(
                    "child" to "btn_text",
                    "variant" to "primary",
                    "action" to mapOf(
                        "event" to mapOf(
                            "name" to "submit_form",
                            "context" to mapOf("username" to mapOf("path" to "/user/name")),
                        ),
                    ),
                ),
            ),
            A2uiComponentPayload("btn_text"),
        ),
        // Stub the required child component
        componentStubs = listOf(
            A2uiComponentStub.withId("btn_text") { _, modifier ->
                Text("Submit", modifier = modifier)
            },
        ),
        // Provide initial dynamic data
        initialData = mapOf("user" to mapOf("name" to "Test User")),
    )

    // 2. Start background processing and initialize the surface
    val surface = controller.start()

    // 3. Mount the UI
    setContent {
        A2uiTestSurface(surface)
    }

    // 4. Interact using standard Compose UI semantics
    onNodeWithText("Submit").performClick()

    // 5. Wait for Compose and A2UI background processes to settle
    waitForIdle()
    controller.waitForIdle()

    // 6. Assert outbound actions were correctly evaluated and intercepted
    val action = controller.dispatchedActions.single() as A2uiEventAction
    assertEquals("submit_form", action.eventName)
    assertEquals("Test User", action.context["username"])
}

Surface states

You can test surface hosts such as A2uiSurface, including their states and transitions:

@Test
fun surface_displaysLoading_thenTransitionsToContent() = runComposeUiTest {
    // 1. Create an empty controller to simulate a pending network request
    val controller = A2uiTestController(
        catalog = CustomComponentCatalog,
        // Pre-register a stub for the expected root component type
        componentStubs = listOf(
            A2uiComponentStub.withType("RootLayout") { _, modifier ->
                Text("Content Ready", modifier = modifier)
            },
        ),
    )
    val surface = controller.start()

    // 2. Mount the surface UI
    setContent {
        A2uiSurface(surfaceModel = surface)
    }

    // 3. Assert the loading placeholder is active
    onNode(hasProgressBarRangeInfo(ProgressBarRangeInfo.Indeterminate)).assertExists()

    // 4. Simulate the agent pushing the layout payload over the network
    controller.updateComponent(
        id = "root",
        type = "RootLayout",
        properties = emptyMap(),
    )

    // 5. Wait for the data layer and animation to settle
    controller.waitForIdle()
    waitForIdle()

    // 6. Assert the loading state is gone and content is visible
    onNode(hasProgressBarRangeInfo(ProgressBarRangeInfo.Indeterminate)).assertDoesNotExist()
    onNodeWithText("Content Ready").assertIsDisplayed()
}

Two-way binding

You can test components like text fields that write back to the data model during user input and verify reactive updates when the agent mutates the data model:

@Test
fun textField_writesToDataModelAndReactsToAgent() = runComposeUiTest {
    val controller = A2uiTestController(
        catalog = CustomComponentCatalog,
        initialComponents = listOf(
            A2uiComponentPayload(
                id = "root",
                type = "TextField",
                properties = mapOf(
                    "label" to "Username",
                    "value" to mapOf("path" to "/form/username"),
                ),
            ),
        ),
        initialData = mapOf("form" to mapOf("username" to "Initial")),
    )
    val surface = controller.start()

    setContent {
        A2uiTestSurface(surface)
    }

    // 1. User interaction updates the global DataModel locally
    onNodeWithText("Initial").performTextReplacement("LocallyTyped")
    waitForIdle()

    // 2. Assert the component wrote back to the DataModel
    assertEquals("LocallyTyped", controller.getData<String>("/form/username"))

    // 3. Simulate the agent pushing a data update for the same path
    controller.updateData("/form/username", "ServerOverridden")
    controller.waitForIdle()

    // 4. Assert the component reactively updated the UI
    onNodeWithText("ServerOverridden").assertIsDisplayed()
}

Components with templated children

You can test components designed to display collections of children defined using A2UI ChildList templates:

@Test
fun column_rendersDynamicChildTemplates() = runComposeUiTest {
    val controller = A2uiTestController(
        catalog = CustomComponentCatalog,
        initialData = mapOf(
            "catalog" to mapOf(
                "products" to listOf(
                    mapOf("title" to "Camera"),
                    mapOf("title" to "Laptop"),
                ),
            ),
        ),
        initialComponents = listOf(
            A2uiComponentPayload(
                id = "root",
                type = "Column",
                properties = mapOf(
                    "children" to mapOf(
                        "path" to "/catalog/products",
                        "componentId" to "product_template",
                    ),
                ),
            ),
            // Bind the initial properties for the dynamically instantiated
            // template stub.
            A2uiComponentPayload(
                id = "product_template",
                properties = mapOf("title" to mapOf("path" to "title")),
            ),
        ),
        componentStubs = listOf(
            A2uiComponentStub.withId(id = "product_template") { props, modifier ->
                val titleProp = remember { A2uiProperty.dynamicString("title") }
                val title = props.bind(titleProp) ?: "Unknown"
                Text(text = "Stubbed: $title", modifier = modifier)
            },
        ),
    )
    val surface = controller.start()
    setContent { A2uiTestSurface(surface) }

    // Verify the template was instantiated twice with relative data
    onNodeWithText("Stubbed: Camera").assertExists()
    onNodeWithText("Stubbed: Laptop").assertExists()

    // Simulate appending a new item to the data model array
    controller.updateData("/catalog/products/-", mapOf("title" to "Tablet"))
    controller.waitForIdle()

    // Verify the Column dynamically instantiated a new child stub
    onNodeWithText("Stubbed: Tablet").assertExists()
}

Error fallbacks for agent errors

You can verify that surfaces and components handle agent errors, such as hallucinations, gracefully:

@Test
fun surface_displaysErrorFallback_onAgentHallucination() = runComposeUiTest {
    val controller = A2uiTestController(catalog = CustomComponentCatalog)
    val surface = controller.start()

    // 1. Mount the surface orchestrator with error boundaries
    setContent { A2uiSurface(surfaceModel = surface) }

    // 2. Simulate an agent hallucinating a broken component layout
    controller.failComponent(
        id = "root",
        exception = A2uiException.A2uiValidationException(
            message = "HallucinatedType",
            path = "/components/root"
        ),
    )
    controller.waitForIdle()

    // 3. Assert the surface displayed the fallback error state
    onNodeWithText("Failed to load: HallucinatedType").assertIsDisplayed()

    // 4. Assert the core layer dispatched an error to the server
    val errorMsg = controller.outboundErrors.single()
    assertEquals("VALIDATION_FAILED", errorMsg.code)
}

Progressive rendering

You can test intermediate states where a parent component has loaded but child components are still pending:

@Test
fun progressiveRendering_parentRendersWhileChildIsPending() = runComposeUiTest {
    // 1. Mount the parent, omitting the child instance
    val controller = A2uiTestController(
        catalog = CustomComponentCatalog,
        initialComponents = listOf(
            A2uiComponentPayload(
                id = "root",
                type = "Button",
                properties = mapOf(
                    "child" to "delayed_text_id",
                    "action" to mapOf("event" to mapOf("name" to "click")),
                ),
            ),
        ),
    )
    val surface = controller.start()
    setContent {
        A2uiTestSurface(surface)
    }

    // 2. Initial state: parent is rendered, child displays loading state
    onNodeWithText("Submit").assertDoesNotExist()
    onNode(hasProgressBarRangeInfo(ProgressBarRangeInfo.Indeterminate)).assertExists()

    // 3. Simulate arrival of the child component
    controller.updateComponent(
        id = "delayed_text_id",
        type = "Text",
        properties = mapOf("text" to "Submit"),
    )
    controller.waitForIdle()

    // 4. Assert that progressive rendering completed
    onNode(hasProgressBarRangeInfo(ProgressBarRangeInfo.Indeterminate)).assertDoesNotExist()
    onNodeWithText("Submit").assertIsDisplayed()
}

Implementation details

The following sections explain component overrides, schema validation, and coroutine synchronization in the test framework.

The testing library introduces the following primary APIs:

  • A2uiTestController: Extension constructor functions and main test controller interface.
  • A2uiComponentStub: Stubs and overrides for child and catalog components.
  • A2uiTestSurface: A lightweight composable utility that mounts a test surface.

Component overrides versus standard mocking

To eliminate heavy third-party mocking frameworks, child components and external dependencies are bypassed using UI stubs (A2uiComponentStub). A2uiComponentStub.withId intercepts a specific component instance by ID, while A2uiComponentStub.withType overrides rendering for an entire catalog type.

Fail-fast schema validation

The test framework enforces the A2UI protocol contract synchronously. When the controller initializes or updates components, it runs A2uiCoreSchemaValidator against provided payloads. If an invalid property is set, such as a missing required field or type mismatch, the test crashes immediately with an A2uiValidationException.

Coroutine synchronization

A2uiTestController.start hooks into the test coroutine context provided by runComposeUiTest(). It extracts currentCoroutineContext(), maps background loops to a detached Job, and automatically cancels itself when the test block completes, preventing dangling test executions. waitForIdle() waits for all pending background coroutines to finish.

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