e2e tests: wait for first compilation

[AlexandreBonaventure]

Hi,
Thanks for the package, it is great!
I'm trying to setup e2e tests with SSR with Cypress. The official e2e-cypress-cli-plugin does not allow to specify to run an alternative command to 'serve' (here ssr:serve) so I overcame the problem by creating a custom service such as :

module.exports = (api, opts) => {
  api.registerCommand('test:e2e:ssr', async (args, rawArgs) => {
    const server = await api.service.run('ssr:serve')
    args.url = 'http://localhost:8080'
    const runner = await api.service.run('test:e2e', args, rawArgs)
    runner.on('exit', () => server.close())
    runner.on('error', () => server.close())
    return runner
  })
}

Problem

ssr:serve signature is pretty different from the traditional serve and this code up there ⬆️ wasn't await the initial compilation like you would expect from serve.

PR

In order to be able to wait for the initial compilation before starting e2e tests, I had to return the readyPromise from the app middleware.