Do not attempt to start the server when usedPortAction is ignore and isPortTaken is true

[brandonaaron]

Summary

I have a dev server already running and used usedPortAction: 'ignore' but the server is still attempted to be started despite the port showing as being taken. This patch puts a fork in the code to not attempt to start the server if ignore is used and isPortTaken is true.

Test plan

Start a server on a given port. Then attempt to use the same port in jest-dev-server config using usedPortAction: 'ignore'. Without the patch, the code will throw an EADDRINUSE error. This is because it will still attempt to run the given command. With the patch, it will simply run the tests.

Workaround

For now, I'm just trapping the EADDRINUSE error for my command (in this specific case it is an express.js server):

  command: `node -e "server = require('./server');server.listen(${config.get('ports.server')}).on('error', (err) => { if (err.code !== 'EADDRINUSE') throw new Error(err) })"

[gregberge]

Hello @brandonaaron, thanks for this, I think it is great but it adds a lot of complexity in the code. @xiaoyuhen do you have ideas to refactor it?

[xiaoyuhen]

😢I can't think of a better solution, maybe and some comments will be easy to understand.

[gregberge]

@xiaoyuhen OK then, we can merge it.