Use doubles only now

Test Doubles
A test double is an object that stands in for another object in your
system
during a code example. Use the double method to create one:

double_account = double("Account")
You can also use the mock and stub methods to create test doubles,
however
these methods are there for backward compatibility only and will likely
be
deprecated and then removed from future versions.
Merge pull request #2 from gutefrage/use_doubles_everywhere

Use doubles only now