Test Double

• Like stunt double, but for testing.
• For testing purposes, test double does the job of the code on which your code under test depends.

Types of Test doubles

Stub

Provides “indirect input”

1. Test places desired return value in stub
2. Stub returns the desired value to the code under test

CLASS ltd_stub DEFINITION FOR TESTING.
  PUBLIC SECTION.
    INTERFACES if_cash_provider PARTIALLY IMPLEMENTED.
    DATA m_notes TYPE if_cash_provider=>tt_change.
ENDCLASS.
        
CLASS ltd_stub IMPLEMENTATION.
  METHOD if_cash_provider~get_notes.
    r_notes = m_notes.
  ENDMETHOD.
ENDCLASS.

Spy

Logs the “indirect output”

1. Spy logs the value passed by the code under test
2. Test verifies the recorded value

CLASS ltd_spy DEFINITION FOR TESTING.
    PUBLIC SECTION.
    INTERFACES if_cash_provider PARTIALLY IMPLEMENTED.
    DATA m_currency TYPE string.
ENDCLASS.

CLASS ltd_spy IMPLEMENTATION.
    METHOD if_cash_provider~get_notes.
    m_currency = i_currency.
    ENDMETHOD.
ENDCLASS

Fake

Simple implementation of depended-on component

Mock

Extension of stub, spy, and fake; verifies the “indirect input” and/or “indirect output” according to given expectations

1. Test places desired value in mock
2. Spy logs the value passed by the code under test
3. Stub returns the desired value to the code under test
4. Test verifies the recorded value

CLASS ltd_mock DEFINITION FOR TESTING.
    PUBLIC SECTION.
    INTERFACES if_cash_provider PARTIALLY IMPLEMENTED.
    DATA m_currency TYPE string.
    DATA m_currency_exp TYPE string.
    DATA m_notes TYPE if_cash_provider=>tt_change.
ENDCLASS.

CLASS ltd_mock IMPLEMENTATION.
    METHOD if_cash_provider~get_notes.
    m_currency = i_currency.
    r_notes = m_notes.
    ENDMETHOD.
    METHOD assert_expectations.
    cl_abap_unit_assert=>assert_equals(
    act = m_currency
    exp = m_currency_exp ).
    ENDMETHOD.
ENDCLASS.

Dummy

Satisfies syntax requirements; does nothing

References

Terminology from the book xUnit Test Patterns, Gerard Meszaros