RSpec tests for a cash flow model
First thing: congratulations on starting with rspec! Way to go. 

My first remark would be to remove your three first contexts (Fields, Associations &amp; Validations). 

Why? Because those are not testing any parts of your code - they are testing ActiveModel functionalities. You want to test your code, not your librairies - at least, not without a very good reason to think that there is a problem there. This is time spent to write specs that do not provide any benefits.

On the other side, while your model don't have much logic yet, I like the fact that you tested your scopes - this is your logic, and it should be tested.