General instruction on running and debugging web_tests can be found here.
Unlike on other platforms, where tests are directly invoked via the blink test script, Fuchsia layers on top its own test script, which handles preparation such as installing the content_shell binary.
Currently, only a small subset of web tests can be run on Fuchsia. Build the target blink_web_tests first before running any of the commands below:
The test script brings up an emulator, runs the tests on it, and shuts the emulator down when finished.
$ <output-dir>/bin/run_blink_web_tests
$ <output-dir>/bin/run_blink_web_tests --target-id=<device-target-id>