ax_client, a test-only out-of-process accessibility client for Windows, is used by browser tests to interact with a window's accessibility tree using either the UI Automation (UIA) or IAccessible2 (IA2) APIs. Tests can use it to evaluate scenarios where an accessibility tool (e.g., a screen reader) performs specific operations against the browser under test.
ax_client.exe is launched from a browser test via an ax_client::Launcher and driven via the interface defined in ax_client.test-mojom.
The launcher redirects the client‘s stdout and stderr to the parent test process’s respective streams so that LOG statements in the client are included in tests' output.
The ax_client::mojom::AxClient interface is meant to be extended with new functionality as needed by tests. Developers should not shy away from adding new methods.
Tests will typically derive from BrowserTestWithAxClient, which includes methods for launching and interacting with ax_client.