Isolated Component Test

This is a test of the create_nested_environment and launch_component_in_nested_environment function in fuchsia_component. Its goal is to ensure the following:

A nested environment is successfully created.
The add_proxy_service function successfully proxies a loader for the new environment, allowing components to be launched.
The add_proxy_service_to function successfully proxies a FIDL service implemented within the environment to other components within the environment.
Components can be brought up in the nested environment.
Components inside the nested environment only have access to the specific set of services granted by their parent, and cannot access other services within their parents' environment. Services added to the nested environment must also be visible to the components inside the nested environment.

The test ensures this by running four separate components.

fuchsia_component_test_outer_component simulates the “outer world”. It spawns fuchsia_component_test_middle_sibling_component which exposes an implementation of EchoExposedBySibling to the nested environment, which multiplies all inputs by 2. It then runs fuchsia_component_test_middle_component in the nested environment containing EchoExposedByParent and EchoHiddenByParent, each of which echos a number and returns it to the client.
fuchsia_component_test_middle_component simulates a parent component attempting to create an isolated child. After confirming that it can successfully access EchoExposedByParent, EchoExposedByParent, and EchoHiddenByParent, it launches fuchsia_component_test_inner_component in a nested environment that only has access to EchoExposedByParent, which has been overridden to always return ‘42’.
fuchsia_component_test_inner_componnent simulates the isolated child component. It confirms that it can't access EchoHiddenByParent or EchoExposedBySibling, and that EchoExposedByParent has been successfully overwritten, always returning ‘42’.

Running the test

fx test fuchsia_component_test_outer