Test Doubles @AlfredoCasado

Object oriented system

storage

messaging

Object oriented system

storage

messaging

Object oriented system

storage

messaging

Object oriented system

storage

messaging

Object oriented system

storage

messaging

Object oriented system

storage

messaging

Problem: test only a selected subset of elements

storage

messaging

Solution: use test doubles to isolate

STUBS● Use stubs to simulate inputs to your system

under test.● In BDD terminology, stubs helps in the given

part of the test.

Example: calculating a student's grade point average

averageGrade(student)stub

grades(student)

OOP: 8,Algorithms: 6,FP: 6,Databases: 10

7,5

Code example (groovy with spock)

def "calculate average grade"() { given: def stub = Mock(GradesRepository) { grades('alfredo') >> [OOP: 8,algorithms: 6,FP: 6,databases: 10] }

def gradesEvaluator = new GradesEvaluator(gradesRepository: stub)

expect: gradesEvaluator.averageGrade('alfredo') == 7.5

}

stub creation

Code example (groovy with spock)

def "calculate average grade"() { given: def stub = Mock(GradesRepository) { grades('alfredo') >> [OOP: 8,algorithms: 6,FP: 6,databases: 10] }

def gradesEvaluator = new GradesEvaluator(gradesRepository: stub)

expect: gradesEvaluator.averageGrade('alfredo') == 7.5

}

stub injection

Mocks/Spies● Use mocks/Spies to verify outputs of your system under

test.● In BDD terminology, mocks/spies helps in the then part

of the test.● With mocks you set expectations before call the SUT,

this are usually “strict” expectations and no other interactions with the double are allowed.

● With spies you check the interactions with the double after call the SUT.

Example: Domotic system

activateSecurity()

WindowsMockclose()

close() DoorsMock

output you want to verify

Code example with mocks (java & jmock)

@Test public void test_activate_security() { final WindowController windowMock = context.mock(WindowController.class); final DoorsController doorsMock = context.mock(DoorsController.class); context.checking(new Expectations() {{ oneOf(windowMock).close(); oneOf(doorsMock).close(); }}); DomoticSystem domotic = new DomoticSystem(windowMock, doorsMock); domotic.activateSecurity(); context.assertIsSatisfied(); }

mocks creation

@Test public void test_activate_security() { final WindowController windowMock = context.mock(WindowController.class); final DoorsController doorsMock = context.mock(DoorsController.class); context.checking(new Expectations() {{ oneOf(windowMock).close(); oneOf(doorsMock).close(); }}); DomoticSystem domotic = new DomoticSystem(windowMock, doorsMock); domotic.activateSecurity(); context.assertIsSatisfied(); }

Code example with mocks (java & jmock)

set expectations

@Test public void test_activate_security() { final WindowController windowMock = context.mock(WindowController.class); final DoorsController doorsMock = context.mock(DoorsController.class); context.checking(new Expectations() {{ oneOf(windowMock).close(); oneOf(doorsMock).close(); }}); DomoticSystem domotic = new DomoticSystem(windowMock, doorsMock); domotic.activateSecurity(); context.assertIsSatisfied(); }

Code example with mocks (java & jmock)

verify interactions

@Test public void test_activate_security() { WindowController windowSpy = mock(WindowController.class); DoorsController doorsSpy = mock(DoorsController.class); DomoticSystem domotic = new DomoticSystem(windowSpy, doorsSpy); domotic.activateSecurity(); verify(windowSpy).close(); verify(doorsSpy).close(); }

Code example with spies (java & mockito)

spy creation

Code example with spies (java & mockito)

@Test public void test_activate_security() { WindowController windowSpy = mock(WindowController.class); DoorsController doorsSpy = mock(DoorsController.class); DomoticSystem domotic = new DomoticSystem(windowSpy, doorsSpy); domotic.activateSecurity(); verify(windowSpy).close(); verify(doorsSpy).close(); }

verify interactions

Recommendations● Test features not methods or classes● Kent Beck definition of unit test is a test that

can run in isolation from other test. A unit test is not test a class in isolation.

● Don’t use test doubles for Value Objects● Don’t use test doubles for types you don’t

own