Question

I am writing unit tests for a simple user model in rails and just started thinking about how I write tests.

There seems to be positive testing:

test "password should match the password_confirmation " do
    user = User.new(
    :email => "[e-mail]",
    :password => "password",
    :password_confirmation => "password")
    assert user.valid?, "did not save user even though password matches confimation"
  end

and negative testing:

test "password should not be valid with mismatching password_confirmation " do
    user = User.new(
    :email => "[e-mail]",
    :password => "password",
    :password_confirmation => "doesnotmatch")
    assert user.invalid?, "saved user with mismatching password_confirmation"
  end

Is it superfluous to include both tests in your test suite or is it a good practice?

Answer 1

Have a look at TDD. When you can move on?, that explains when you are ready with your tests (and code) and can move on. In you example, that means:

• You first write the positive test. The test fails.
• You then write the necessary code so that the test succeeds.

• After that, you need another test to prove that your implementation is not sufficient. When you have written e.g.

  class User
    def initialize(hash)
      @hash = hash
    end
    def valid?
      true
    end
  end
  

  you need another test case to prove that wrong.

• Write the next test case, that shows that checking the password can fail.

I see the following cases:

• No password
• Matching passwords (but too short)
• Matching passwords (long and difficult enough)
• Not matching password

So you would need 4 test cases for that.