Did a project to help out a friends friend and got recommended. As soon as I've got a job offer I took it. I don't really think you can define job ready in any meaningful way. I guess you're good at it as soon as you've tested. This is the way I did it but I might be a fraud.
If you want to know for sure. Do a project for free or for a ridiculous low price. If you succeed you have one data point towards a somewhat reliable answer. Then again if it goes south it might to be some other factor as well.