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Integration testing topologies

Integration testing scenarios involve two or more components operating in the same realm and exchanging capabilities. While the majority of tests are unit tests that span only a single component, integration testing scenarios call for defining realm topologies and capability routes.

In cases where all components in the test are static, you can define the topology for the test realm in the test component manifest. In cases where realm topology needs to be defined at runtime, or components need to be mocked out, Realm Builder should be used.

Component topology

The integration test component declares the topology of the test realm with itself as the parent. This allows the test controller to be responsible for capability routing between components under test and their dependencies.

The following is an example topology for integration testing the echo_server component:

Integration test topology

This is a simple test realm that binds to the fidl.examples.routing.echo.Echo protocol exposed by the echo_server component. The echo_integration_test package contains the following components:

  • echo_integration_test - Test controller
  • echo_server - Component under test
    // ...

    // Child components orchestrated by the integration test.
    children: [
            name: "echo_server",
            url: "#meta/",

    // Capabilities used by this component.
    use: [
            protocol: [ "fidl.examples.routing.echo.Echo" ],
            from: "#echo_server",

    // Capabilities required by components under test.
    offer: [
            protocol: [ "fuchsia.logger.LogSink" ],
            from: "parent",
            to: "#echo_server",

The test controller component contains the test case logic, and interacts with the echo_server through its exposed capabilities.

Test Runner Framework integration

The integration test component includes test_runners/rust/default.shard.cml in order to integrate with the Test Runner Framework. This shard provides two key elements:

  1. Expose the fuchsia.test.Suite protocol, required for the framework to discover and execute the test cases.
  2. Set the program runner to the Rust test runner, required to execute test cases using the Rust testing framework.

Build definition

See the following file that defines the fuchsia_test_package() target for this example:

rustc_test("bin") {
  name = "echo_integration_test"
  edition = "2018"

  deps = [

  sources = [ "src/" ]

fuchsia_component("echo_integration_test_component") {
  testonly = true
  component_name = "echo_integration_test"
  manifest = "meta/echo_integration_test.cml"
  deps = [ ":bin" ]

fuchsia_test_package("echo_integration_test") {
  test_components = [ ":echo_integration_test_component" ]
  deps = [ "//examples/components/routing/echo_server:echo_server_component" ]

All components under test are included in the same hermetic test package. This promotes the ability to run and update tests in different environments without concern for dependencies falling out of sync.

Determining a component's moniker

The ArchiveReader library allows your test to validate data in Inspect. The moniker for a component is always relative to the root realm. For a component running in a test, the moniker is therefore the name field defined in the test root. In the example above, the moniker for the echo_server is simply echo_server.

See the Inspect Codelab for detailed information on using ArchiveReader.