start use ffaker and refact some tests

[gabrielbaldao]

Resolves #1

Description

I'm trying improve the tests in this project with best pratices, we can improve together and write more tests.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not
  work as expected)

[cflipse]

Couple of things:

• Can you give a quick explanation of the difference between faker and ffaker ?

• Please keep commits separated into a single idea. If you're going to add a new gem, do that in a single commit, and a second -- or sequence of -- commit that modifies usage to use the new gem.

• if you're going to remove a gem, that too should be it's own commit, once the migration commits have been applied. And you should probably check that it's not in use elsewhere. (this is a hint)

• I acutally strongly prefer not to use the FactoryBot syntax mixins. The data generator source should be abundantly clear while reading the specs.

Otherwise, this looks good