You always end up coming to it. It's inevitable. It cannot be helped. Yep, it's time to write a custom validator for your shiny new Angular application. So how do you do that in Angular 4? And more importantly: how do you test it?
It's might not be a well-know feature, but AngularJS allows you to use the ng-required argument on input and textarea fields. And that can be quite handy!
So you want to validate the data sent to your application's REST services? Nowadays you can quite easily do that using Spring and the Bean Validation API. And to help you test that validation process, how about bringing in Spring Boot to programmatically start your application and run your tests against it?