Is my assumption of test driven development correct?

Hello Joel!

You are definitely not wrong in how you see it.

Think of test driven development as being a proactive approach to a situation, rather than reacting as the issues occur.

Assuming all your prep work is done (planing the app, what is should do, what will or can go wrong, etc) your next step in TDD would be to add your first test, run your test, if failure make small changes, run again, fail make another small change. Once you have made minimal changes with compliant code you move on in development until all steps are given a green light.

Brian explained TDD, so I have nothing to add to it, so let me explain the code you asked about:

test "a user should have a unique profile name" do - this is the description of the test

user = User.new - this creates a new object of class User and names the object user

user.profile_name = users(:someguy).profile_name - user's profile_name is set to the profile name of another, existing user

assert !user.save - we assert that our object user will not be saved to the database, because his name is the same as the name of another user that is already in the database

assert !user.errors[:profile_name].empty? - we assert that there will be errors associated with profile_name when trying to save our user in the database

Unfortunately, this code is not as readable as RSpec code, that's why a lot of Rails developers don't use the default testing framework and instead use the RSpec gem for tests (Treehouse's Todo List application course uses RSpec if you want to see it in action).