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CDP

Lab can run tests that use browser-backed FQL, but Lab does not own browser execution or Chrome DevTools Protocol behavior. That belongs to the selected Ferret runtime.

In current Lab v2, there is no --cdp flag and no LAB_CDP environment variable. Configure browser access through the Ferret runtime and FQL options you are using.

Browser-backed tests

A browser-backed test is still a normal Lab test file. The external host must register the web::html module and the CDP driver used by this example:

example.fql
read-only
let doc = web::html::open("https://example.com", { driver: "cdp" }) return doc.title

Start an external host with those capabilities, then select it in Lab:

terminal 
lab run --runtime=wire+tcp://127.0.0.1:50051 browser.fql

If the runtime expects an existing browser endpoint, start that browser separately and make sure the runtime can reach it.

Wait for a browser endpoint

Use --wait when a browser endpoint is started outside Lab and may not be ready yet.

terminal 
lab run browser-tests/ \  --runtime=wire+tcp://127.0.0.1:50051 \  --wait=http://127.0.0.1:9222/json/version \  --wait-timeout=5 \  --wait-attempts=12

The wait happens before tests execute. It does not configure the runtime; it only prevents tests from starting before the dependency responds.

Builtin runtime

The builtin runtime runs Ferret core and its standard library inside the Lab process. It does not register optional browser modules or a CDP driver. Use an HTTP or Wire host configured with the required module and driver for browser-backed tests. Lab passes user parameters and @lab system parameters into that host without rewriting browser options.

HTTP and Wire runtimes

When you use --runtime=http(s)://... or --runtime=wire+tcp://127.0.0.1:<port>, browser connectivity is evaluated from that runtime’s environment.

For example, if Lab runs on your laptop but the HTTP runtime runs in a container, 127.0.0.1:9222 inside the query refers to the runtime container, not your laptop. Expose or advertise the browser endpoint in a way that the runtime can reach.

The same rule applies to Lab local services. If a remote runtime must fetch @lab.static or @lab.mock URLs, set --serve-bind and --serve-host so those URLs are reachable from the runtime.

For Lab-owned local service flags, see Static File Server and Mock API Server.

CI pattern

A common CI shape is:

  1. Start the browser or runtime service.
  2. Use lab run --wait=... to wait for its health endpoint.
  3. Run tests with --reporter=simple.
terminal 
lab run browser-tests/ \  --runtime=wire+tcp://127.0.0.1:50051 \  --wait=http://127.0.0.1:9222/json/version \  --reporter=simple

Next steps

Remote runtime HTTP Runtime Run tests against a remote Ferret HTTP runtime. Remote runtime Wire Runtime Run tests through the hosted Universal Ferret API over gRPC. Test execution Running Tests Run local, HTTP, and Git-hosted test files with parameters and waits.