Handling failed assertions

[ju5t]

At the moment when an assertion fails it throws a ProcessFailedException. This helps when debugging PR's, but it's probably not something we'd like to do for the first release of this package.

A solution could be to try/catch it:

try {
    $process = new Process(['npx', 'playwright', 'test', '--reporter=json']);

    $process->mustRun();

    $output = $process->getOutput();
} catch (ProcessFailedException) {
    return new TestResult(false);
}

Doing this in the worker would solve it; but it returns a pretty obscure error:

Failed asserting that false is true

I haven't made the PR for this just yet because of it, but also curious what others think of it.