custom validation section needs more info about activerecord-validations-lab

[darrendaz]

Wouldn't have guessed the solution for the custom validation. Documentation searched and read so far doesn't contain details on this usage either oof.

[sgharms]

@brittanytinnin

We updated the documentation to give a hint in be48b7e based on your suggestion. We're going to do a bigger pass on this entire topic in end 2019, but wanted to address this issue now.

Validations can be tested by using custom Rails extensions to RSpec. Here's a good guide: https://til.hashrocket.com/posts/af87b1eaa8-test-validation-errors-with-rspec

@darrendaz Your concern should be addressed by the change as well.