Test doubles (Java/Mockito)

Slide 1

Slide 1 text

Test doubles (stubs and mocks)

Slide 2

Slide 2 text

TDD

Slide 3

Slide 3 text

TDD

Slide 4

Slide 4 text

TDD

Slide 5

Slide 5 text

Refactoring

Slide 6

Slide 6 text

Refactoring

Slide 7

Slide 7 text

Refactoring

Slide 8

Slide 8 text

Queries & commands (a small digression)

Slide 9

Slide 9 text

Queries User  repository Authenticator Session

Slide 10

Slide 10 text

Queries User  repository Authenticator Session findUser("bob");

Slide 11

Slide 11 text

Queries User  repository Authenticator Session [a User object]

Slide 12

Slide 12 text

Commands User  repository Authenticator Session setUser(user);

Slide 13

Slide 13 text

Test doubles (stubs & mocks)

Slide 14

Slide 14 text

Stubbing a query Stub  repository Authenticator Session findUser("bob");

Slide 15

Slide 15 text

Stubbing a query Stub  repository Authenticator Session [a User object]

Slide 16

Slide 16 text

A stub simply returns canned values

Slide 17

Slide 17 text

A stub simply returns canned values ! (which may be real value objects or other test doubles)

Slide 18

Slide 18 text

Mocking a command User  repository Authenticator Mock  Session setUser(user);

Slide 19

Slide 19 text

A mock veriﬁes methods were called

Slide 20

Slide 20 text

Stub queries Mock commands

Slide 21

Slide 21 text

Outside-in design

Slide 22

Slide 22 text

Identify responsibilities

Slide 23

Slide 23 text

Identify responsibilities Does the class have a single responsibility?

Slide 24

Slide 24 text

Identify responsibilities Does the class have a single responsibility? Yes test drive behaviour as normal

Slide 25

Slide 25 text

Identify responsibilities Does the class have a single responsibility? Yes test drive behaviour as normal No identify collaborating roles (interfaces) specify interactions using test doubles

Slide 26

Slide 26 text

Implement collaborators

Slide 27

Slide 27 text

Implement collaborators For each role identiﬁed at the layer above…

Slide 28

Slide 28 text

Implement collaborators For each role identiﬁed at the layer above… Identify responsibilities Does the class have a single responsibility? Yes test drive behaviour as normal No identify collaborating roles (interfaces) specify interactions using test doubles

Slide 29

Slide 29 text

Rules*

Slide 30

Slide 30 text

Rules* A class can arrange collaborators or do work

Slide 31

Slide 31 text

Rules* A class can arrange collaborators or do work Stub queries; mock commands

Slide 32

Slide 32 text

Rules* A class can arrange collaborators or do work Stub queries; mock commands Doubles can return value objects or other doubles (but not objects with behaviour)

Slide 33

Slide 33 text

Slide 34

Slide 34 text

Rules* A class can arrange collaborators or do work Stub queries; mock commands Doubles can return value objects or other doubles (but not objects with behaviour) Don’t stub or mock value objects or primitives Don’t stub or mock the object under test

Slide 35

Slide 35 text

Slide 36

Slide 36 text

Slide 37

Slide 37 text

Show me the code!

Slide 38

Slide 38 text

Java frameworks

Slide 39

Slide 39 text

Java frameworks EasyMock

Slide 40

Slide 40 text

Java frameworks EasyMock JMock

Slide 41

Slide 41 text

Java frameworks EasyMock JMock Mockito

Slide 42

Slide 42 text

Java frameworks EasyMock JMock Mockito JMockit

Slide 43

Slide 43 text

Java frameworks EasyMock JMock Mockito JMockit PowerMock

Slide 44

Slide 44 text

Java frameworks EasyMock JMock Mockito JMockit PowerMock

Slide 45

Slide 45 text

Stubbing

Slide 46

Slide 46 text

Stubbing import static org.mockito.Mockito.*;

Slide 47

Slide 47 text

Stubbing import static org.mockito.Mockito.*; Widget widget = mock(Widget.class);

Slide 48

Slide 48 text

Stubbing import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); when(widget.foo(0)).  thenReturn("something");

Slide 49

Slide 49 text

Stubbing import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); when(widget.foo(0)).  thenReturn("something"); when(widget.foo(anyInt())).  thenReturn("something else");

Slide 50

Slide 50 text

Stubbing import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); when(widget.foo(0)).  thenReturn("something"); when(widget.foo(anyInt())).  thenReturn("something else"); when(widget.bar(any())).  thenThrow(new RuntimeException());

Slide 51

Slide 51 text

Mocking

Slide 52

Slide 52 text

Mocking import static org.mockito.Mockito.*;

Slide 53

Slide 53 text

Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class);

Slide 54

Slide 54 text

Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); // do some stuff

Slide 55

Slide 55 text

Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); // do some stuff verify(widget).foo(1);

Slide 56

Slide 56 text

Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); // do some stuff verify(widget).foo(1); verify(widget).bar();

Slide 57

Slide 57 text

Mocking import static org.mockito.Mockito.*; Widget widget = mock(Widget.class); // do some stuff verify(widget).foo(1); verify(widget).bar(); verify(widget).baz(42, isA(Quuz.class));

Slide 58

Slide 58 text

Exercise Use doubles to test-drive a Transaction class with a transfer method that takes an amount and two Account objects (source and destination). When transfer is called, the source account should receive debit(amount) and the destination account credit(amount).