tests

Look at this code Rails FactoryGirl definition for a regular user class

FactoryGirl.define do
  factory :user do
    first_name "John"
    last_name  "Doe"
    subscription_end_date Date.parse("2019-01-01")
  end
end

Does not look harmful. This is a base model. When your other spec files start using it, everything will work fine when you evaluate the subscription_end_date with other fields, but, exactly after 2019-01-01, on 2nd Jan 2019, the tests dependent on this value will start failing.

Anything that is hard coded when tested with relative time like, before/after (based on when the test is running) will start failing. Either use all relative dates or all absolute dates. Time.zone.now is relative unless you perform a timecop.freeze before hand.

Happy hacking!