Good Unit Testing Practice

A common but misguided practice that is often seen in unit test designs, is to test some kind of a false moniker on an object, rather than the actual properties of the object that should be tested.
For example. We have a simple "Dog" object and we want to get a list of all Dogs of a certain breed,ordered by the date of birth of the dog.

class Dog{

Breed breed;
Date dob;
String name;

}

When testing using this moniker style we might test like this (notice that i have introduced errors but the tests still pass since they are testing the moniker and not the properties that should be tested)...

void testGetAllAlsationsOrderedByAgeUsingMonikers(){

Dog fido = new Dog(name:'alsation born last year', dob: '01/01/2006', breed:Breed.ALSATION)
Dog woofer = new Dog(name:'alsation born 2 years ago', dob:'01/01/2008',breed:Breed.LABRADOR)
Dog mutley = new Dog(name:'alsation born this year', dob: '01/01/2008', breed:Breed.ALSATION)

List dogs = DogService.getDogByBreed(Breed.ALSATION)
assertTrue 'alsation born 2 years ago', dogs[0].name
assertTrue 'alsation born born last year', dogs[1].name
assertTrue 'alsation born this year', dogs[2].name

}

the problem with this is that we are actually not testing for the real properties that we should be testing for, and we are relying on the fact that we didn't introduce any errors in our test set up. which, incidentally,we did, just to prove the point!


A much better way to test this would be the following...

void testGetAllAlsationsOrderedByAgeCorrectly(){

Dog fido = new Dog(name:'not relevant', dob: '01/01/2006', breed:Breed.ALSATION)
Dog woofer = new Dog(name:'not relevant', dob: '01/01/2008', breed:Breed.LABRADOR)
Dog mutley = new Dog(name:'not relevant', dob: '01/01/2008', breed:Breed.ALSATION)

List dogs = DogService.getDogByBreed(Breed.ALSATION)
assertEquals(2, dogs.size())
assertTrue( isOrderedByDateOfBirth( dogs) )
assertTrue ( dogs.every{ Dog dog -> dog.breed=Breed.ALSATION} )

}

private boolean isOrderedByDateOfBirth( List dogs) {

def dobComparator = [compare:{Dog dog1, Dog dog2 ->
dog1.dob == dob2.dob ? 0 :dog1.dob > dog2.dob? 1 : -1 }] as Comparator
return dogs.sort(dobComparator) == dogs

}