Testing FIDL protocols
Prerequisites
This tutorial builds on the HLCPP getting started tutorials.
Overview
This tutorial walks through the process of writing a test for the
Echo.EchoString
method. This tutorial shows you how to use the two utilities
available for testing FIDL protocols implemented in HLCPP:
- The
gtest
test loop fixturesys::testing::ComponentContextProvider
. - The
fidl_test_base.h
file provided by the HLCPP bindings
If you want to write the code yourself, delete the following directories:
rm -r examples/fidl/hlcpp/testing/*
The test will be written in examples/fidl/hlcpp/testing/main.cc
.
Set up dependencies
To set up dependencies:
Include the libraries that are needed for the test:
{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/testing/main.cc" region_tag="includes" %}
Add a build rule for the test in
examples/fidl/hlcpp/testing/BUILD.gn
:{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/testing/BUILD.gn" %}
Create a server implementation
To create a server implementation:
Add an implementation for the
Echo
protocol that is tested:{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/testing/main.cc" region_tag="impl" %}
Rather than inheriting from
fuchsia::examples::Echo
, this implementation inherits from the corresponding test base class. This means that the implementation only needs to override the methods that are being tested (in this case,EchoString
), as well as theNotImplemented_
method, which is called if any of the request handler methods that are not overriden get called.Create a test class that wraps the logic of publishing the echo protocol:
{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/testing/main.cc" region_tag="wrapper" %}
This is similar to the code that is explained in the server tutorial, but the
fidl::Binding
is owned by the class. This makes the binding’s destructor get called when the class is destroyed. This enables the code to publish the echo protocol on each test case given a new instance of the test component context.
Implement the text fixture class
{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/testing/main.cc" region_tag="fixture" %}
The test fixture does the following:
- Holds an instance of a
ComponentContextProvider
. Each test, it uses it to create a new test context, and binds the Echo implementation to it using theEchoServerInstance
class. - Provides a
GetProxy()
method initializes a proxy to the current test component context and returns it.
Add tests
This is an example test that can you can write with the text fixture:
{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/testing/main.cc" region_tag="test" %}
Run the test
To run the test:
Configure your GN build to include the test:
fx set core.x64 --with //examples/fidl/hlcpp/testing
Run the test:
fx test -vo example-hlcpp-protocol-test
You should see the test output indicating a success.
Summary
- The
gtest::TestLoopFixture
removes the need for boilerplate async loop setup code. Each test case can simply callRunLoopUntilIdle()
instead of manually managing anasync::Loop
. - The
ComponentContextProvider
makes it easy to mock the component context during a test. This is useful to e.g. provide specific capabilities to the a component. - The HLCPP bindings test scaffolding provides a test base for each protocol class that has a dummy implementation for each method. This allows tests to only implement the methods under test.