If you have code that uses DateTime.now you ask yourself "How's my test supposed to pass?" and your pair says "I'd peg it at 1 out of ten times" and if your pair is Rohan Kini you know you have a way out.
Let's set it up right. I have this object:
class User
def initialize
@time_of_birth = DateTime.now
@name = "The dude"
end
def take_over_the_world
p "#{self.name} is taking over the world"
end
end
The tests for which look like
def test_if_use_is_born_with_right_defaults
the_dude = User.new
assert_equal the_dude.time_of_birth, DateTime.now
assert_equal the_dude.name, "The dude"
end
Now obviously a few milliseconds might have past since the execution of User.new so odds are your test will fail even though they should pass.
Here's how you change things around a bit.
In your user class you need to abstract the DateTime.now bit, so you can override things in your test
class User
def date
DateTime.now
end
def initialize
@time_of_birth = date
@name = "The dude"
end
def take_over_the_world
p "#{self.name} is taking over the world"
end
end
And in your test override the new date method you created.
NOW = DateTime.now
class << User
def date
NOW
end
end
def test_if_use_is_born_with_right_defaults
the_dude = User.new # Will use now because you've overridden User::date in the context of this test
assert_equal the_dude.time_of_birth, NOW
assert_equal the_dude.name, "The dude"
end
