While fake dependencies are really useful for unit testing, they lack in features like tracking function calls, intercepting arguments, etc.. that makes unit testing easier. Mock dependency is a dependency which offers all the benefits of fake dependencies and more features to make unit testing easier.
It is not going to be easy to create and maintain mock dependencies; this is why we generally use mocking libraries to create mock dependencies.
If we take the same passenger discount example that we have seen previously
module promotions
function isPromotionsAvailable():
.
.
.
module discounts
function isDiscountAvailable(age):
if promotions.isPromotionAvailable() && age > 60:
print("discount available")
else:
print("discount not available")
we create, setup and use mock version of isPromotionAvailable() like this in the tests:
function test_isDiscountAvailable():
// arrange
mockPromotions = mock(promotions) // create mock promotion
mockPromotions.isPromotionAvailable().return(true) // setup the method to return true
promotions = mockPromotions // replace promotions with mockPromotions
age = 65
// act
result = discounts.isDiscountAvailable(age)
Depending on the language and framework we use, the way we create, setup and use mock dependencies will be different.