Assertions of Truth in Ruby Tests

I used to write my assertions like this:

assert user.active?
refute user.inactive?

Then I joined a team where I was encouraged to write this:

assert_equal true, user.active?
assert_equal false, user.inactive?

What? That doesn’t look very nice. That’s doesn’t feel very Ruby. It’s less elegant!

Here’s the thing, though: your unit tests aren’t about being elegant. They’re about guaranteeing correctness. You open the door to some insidious bugs when you test truthiness instead of truth.

• You might perform an assignment rather than comparing equality.

def active?
  # Should be status == :active
  status = :active
end

• You might check the presence of an array, rather than its length.

def has_users?
  # Should be user_list.any?
  user_list
end

def user_list
  []
end

Over time, I’ve gotten used to it. This style still chafes, but not as badly as bugs caused by returning the wrong value from a predicate method.

Comments

[Brandon Weaver]

It's a good idea, because in a lot of Ruby things only have to be "Boolean-like" rather than actually true and false.

In fact there's been a bit of an ongoing debate in the Rails codebase between the two and it can be quite confusing, as one in-particular that presents as Boolean by name can return 0. While that's truthy in Ruby it still creates confusion, even if it is an index position, because of the way the method is presented as boolean.