Slides from my GDC 2014 talk on practical unit testing. How can bad unit tests slow iteration? And how can you fix them?

1. http://tinyurl.com/sf-rnt

2. Unit
Tests
Practical
Andrew Fray, Spry Fox

3. #pracunittests
Test Driven
Development

4. #pracunittests
Backwards Is Forward: Making Better
Games with Test-Driven Development
http://gdcvault.com/play/1013416/Backwards-Is-Forward-Making-Better
Sean Houghton, Noel Llopis
http://tinyurl.com/gddtdd

5. #pracunittests
2004
@tenpn

6. #pracunittests
2004
@tenpn

7. Definitions

8. #pracunittests
Unit TestSingle explicit assumption

9. #pracunittests
Unit TestSingle explicit assumption
Integration Test
Many implicit assumptions

10. #pracunittests
Qualities of Good Unit Tests

11. #pracunittests
Qualities of Good Unit Tests
Readable

12. #pracunittests
Qualities of Good Unit Tests
Readable
Maintainable

13. #pracunittests
Qualities of Good Unit Tests
Readable
Maintainable
Trustworthy

14. Post
Mortem

15. #pracunittests
F1 2011 X360/PS3/PC

16. #pracunittests
F1 2011 X360/PS3/PC
• Isolated new subsystem

17. #pracunittests
F1 2011 X360/PS3/PC
• Isolated new subsystem
• 502 tests, 6700 lines of test code

18. #pracunittests
F1 2011 X360/PS3/PC
• Isolated new subsystem
• 502 tests, 6700 lines of test code
• 6200 lines of production code

19. #pracunittests
A Partial Succes

20. #pracunittests
• Clean, re-usable
code
A Partial Succes

21. #pracunittests
• Clean, re-usable
code
• Fewer bugs
A Partial Succes

22. #pracunittests
• Clean, re-usable
code
• Fewer bugs
• Easy to optimise
A Partial Succes

23. #pracunittests
• Clean, re-usable
code
• Fewer bugs
• Easy to optimise
• At end, treacle-like
progress
A Partial Succes

24. Unit Test
Anti-Patterns

25. #pracunittests
1/4: The Opaque Anti-Pattern

26. #pracunittests
// in LinearDescriptionFixture…
void testBackwardsToNormalLeftwardsGradient() {
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(1f).withInitialValue(10.0f).withOffsetOrigin(0.0f)
.withDirection(Direction.eLeft);
TEST_GREATER(leftDesc.getValueAtOffset(-1.0f), 10.0f);
}
1/4: The Opaque Anti-Pattern

27. #pracunittests
// in LinearDescriptionFixture…
void testBackwardsToNormalLeftwardsGradient() {
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(1f).withInitialValue(10.0f).withOffsetOrigin(0.0f)
.withDirection(Direction.eLeft);
TEST_GREATER(leftDesc.getValueAtOffset(-1.0f), 10.0f);
} wat
1/4: The Opaque Anti-Pattern

28. #pracunittests
Opaque: Hard to see HOW
void testBackwardsToNormalLeftwardsGradient() {
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(1f).withInitialValue(10.0f).withOffsetOrigin(0.0f)
.withDirection(Direction.eLeft);
TEST_GREATER(leftDesc.getValueAtOffset(-1.0f), 10.0f);
}

29. #pracunittests
Opaque: Hard to see HOW
void testBackwardsToNormalLeftwardsGradient() {
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(1f).withInitialValue(10.0f).withOffsetOrigin(0.0f)
.withDirection(Direction.eLeft);
TEST_GREATER(leftDesc.getValueAtOffset(-1.0f), 10.0f);
}

30. #pracunittests
Opaque: Hard to see HOW
void testBackwardsToNormalLeftwardsGradient() {
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(1f).withInitialValue(10.0f).withOffsetOrigin(0.0f)
.withDirection(Direction.eLeft);
TEST_GREATER(leftDesc.getValueAtOffset(-1.0f), 10.0f);
}

31. #pracunittests
Opaque: No Magic Literals

32. #pracunittests
Opaque: No Magic Literals
void testBackwardsToNormalLeftwardsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
float someLeftOfOrigin = someOrigin - 1.0f;
!
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin).withDirection(Direction.eLeft);
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

33. #pracunittests
Opaque: No Magic Literals
void testBackwardsToNormalLeftwardsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
float someLeftOfOrigin = someOrigin - 1.0f;
!
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin).withDirection(Direction.eLeft);
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

34. #pracunittests
Opaque: No Magic Literals
void testBackwardsToNormalLeftwardsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
float someLeftOfOrigin = someOrigin - 1.0f;
!
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin).withDirection(Direction.eLeft);
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

35. #pracunittests
Opaque: No Magic Literals
void testBackwardsToNormalLeftwardsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
float someLeftOfOrigin = someOrigin - 1.0f;
!
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin).withDirection(Direction.eLeft);
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

36. #pracunittests
void testBackwardsToNormalLeftwardsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
float someLeftOfOrigin = someOrigin - 1.0f;
!
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin).withDirection(Direction.eLeft);
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

37. #pracunittests
void testBackwardsToNormalLeftwardsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
float someLeftOfOrigin = someOrigin - 1.0f;
!
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin).withDirection(Direction.eLeft);
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

38. #pracunittests
Opaque: Informative,
Consistent Test Name

39. #pracunittests
Opaque: Informative,
Consistent Test Name
void nameOfFunctionUnderTest_ContextOfTest_DesiredResultOfTest() {

40. #pracunittests
Opaque: Informative,
Consistent Test Name
void nameOfFunctionUnderTest_ContextOfTest_DesiredResultOfTest() {
void testBackwardsToNormalLeftwardsGradient() {

41. #pracunittests
Opaque: Informative,
Consistent Test Name
void nameOfFunctionUnderTest_ContextOfTest_DesiredResultOfTest() {
void
void withDirection_Left_InvertsGradient() {

42. #pracunittests
void withDirection_Left_InvertsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
float someLeftOfOrigin = someOrigin - 1.0f;
!
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin).withDirection(Direction.eLeft);
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

43. #pracunittests
void withDirection_Left_InvertsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
float someLeftOfOrigin = someOrigin - 1.0f;
!
LinearDescription leftDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin).withDirection(Direction.eLeft);
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

44. #pracunittests
Opaque: Arrange-Act-Assert

45. #pracunittests
Opaque: Arrange-Act-Assert
void withDirection_Left_InvertsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
LinearDescription increasingDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin);
!
LinearDescription leftDesc = increasingDesc.withDirection(Direction.eLeft);
!
float someLeftOfOrigin = someOrigin - 1.0f;
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

46. #pracunittests
Opaque: Arrange-Act-Assert
void withDirection_Left_InvertsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
LinearDescription increasingDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin);
!
LinearDescription leftDesc = increasingDesc.withDirection(Direction.eLeft);
!
float someLeftOfOrigin = someOrigin - 1.0f;
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

47. #pracunittests
Opaque: Arrange-Act-Assert
void withDirection_Left_InvertsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
LinearDescription increasingDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin);
!
LinearDescription leftDesc = increasingDesc.withDirection(Direction.eLeft);
!
float someLeftOfOrigin = someOrigin - 1.0f;
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

48. #pracunittests
Opaque: Arrange-Act-Assert
void withDirection_Left_InvertsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
LinearDescription increasingDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin);
!
LinearDescription leftDesc = increasingDesc.withDirection(Direction.eLeft);
!
float someLeftOfOrigin = someOrigin - 1.0f;
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

49. #pracunittests
Opaque: Arrange-Act-Assert
void withDirection_Left_InvertsGradient() {
float someValueAtOrigin = 10.0f;
float someOrigin = 0.0f;
float positiveGradient = 1.0f;
LinearDescription increasingDesc = DefaultFlatLinearDescription()
.withGradient(positiveGradient).withInitialValue(someValueAtOrigin)
.withOffsetOrigin(someOrigin);
!
LinearDescription leftDesc = increasingDesc.withDirection(Direction.eLeft);
!
float someLeftOfOrigin = someOrigin - 1.0f;
float valueToLeft = leftDesc.getValueAtOffset(someLeftOfOrigin);
TEST_GREATER(valueToLeft, someValueAtOrigin);
}

50. #pracunittests
The Opaque Anti-Pattern

51. #pracunittests
The Opaque Anti-Pattern
• Hard to see "how"?

52. #pracunittests
The Opaque Anti-Pattern
• Hard to see "how"?
• Demystify magic literals

53. #pracunittests
The Opaque Anti-Pattern
• Hard to see "how"?
• Demystify magic literals
• Consistent informative test name

54. #pracunittests
The Opaque Anti-Pattern
• Hard to see "how"?
• Demystify magic literals
• Consistent informative test name
• Arrange-Act-Assert

55. #pracunittests
2/4: The Wet Anti-Pattern
RacingLineOffsets.setSignedDistanceToRacingLine(RacingLine, float)

56. #pracunittests
RacingLineOffsets.setSignedDistanceToRacingLine(RacingLine, float, int)
2/4: The Wet Anti-Pattern
RacingLineOffsets

57. #pracunittests
RacingLineOffsets.setSignedDistanceToRacingLine(RacingLine, float, int)
2/4: The Wet Anti-Pattern
> Test library build failed with 235 error(s)
RacingLineOffsets

58. #pracunittests
void getIdealOffset_BeyondRacingLineEdge_ReturnsEdge() {
float someRacingLineRadius = 10.0f;
float someOffsetBeyondRacingLine = someRacingLineRadius + 1.0f;
!
RacingLineOffsets beyondOffsets = new RacingLineOffsets();
float leftRacingLineEdge =
-someRacingLineRadius - someOffsetBeyondRacingLine;
beyondOffsets.setSignedDistanceToRacingLine(
RacingLine.eLeftEdge, leftRacingLineEdge);
beyondOffsets.setSignedDistanceToRacingLine(
RacingLine.eCenter, -someOffsetBeyondRacingLine);
float rightRacingLineEdge =
someRacingLineRadius - someOffsetBeyondRacingLine;
beyondOffsets.setSignedDistanceToRacingLine(
RacingLine.eRightEdge, rightRacingLineEdge);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(beyondOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(idealRacingLineOffset, someRacingLineRadius);
}
void getIdealOffset_WithinRacingLineEdge_ReturnsOffset() {
float someRacingLineRadius = 10.0f;
float someOffsetWithinRadius = someRacingLineRadius * 0.8f;
!
RacingLineOffsets withinOffsets = new RacingLineOffsets();
float leftRacingLineEdge =
-someRacingLineRadius - someOffsetWithinRadius;
withinOfffsets.setSignedDistanceToRacingLine(
RacingLine.eLeftEdge, leftRacingLineEdge);
withinOffsets.setSignedDistanceToRacingLine(
RacingLine.eCenter, -someOffsetWithinRadius);
float rightRacingLineEdge =
someRacingLineRadius - someOffsetWithinRadius;
withinOffsets.setSignedDistanceToRacingLine(
RacingLine.eRightEdge, rightRacingLineEdge);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(withinOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(idealRacingLineOffset, someOffsetWithinRadius);
}

59. #pracunittests
void getIdealOffset_BeyondRacingLineEdge_ReturnsEdge() {
float someRacingLineRadius = 10.0f;
float someOffsetBeyondRacingLine = someRacingLineRadius + 1.0f;
!
RacingLineOffsets beyondOffsets = new RacingLineOffsets();
float leftRacingLineEdge =
-someRacingLineRadius - someOffsetBeyondRacingLine;
beyondOffsets.setSignedDistanceToRacingLine(
RacingLine.eLeftEdge, leftRacingLineEdge);
beyondOffsets.setSignedDistanceToRacingLine(
RacingLine.eCenter, -someOffsetBeyondRacingLine);
float rightRacingLineEdge =
someRacingLineRadius - someOffsetBeyondRacingLine;
beyondOffsets.setSignedDistanceToRacingLine(
RacingLine.eRightEdge, rightRacingLineEdge);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(beyondOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(idealRacingLineOffset, someRacingLineRadius);
}
void getIdealOffset_WithinRacingLineEdge_ReturnsOffset() {
float someRacingLineRadius = 10.0f;
float someOffsetWithinRadius = someRacingLineRadius * 0.8f;
!
RacingLineOffsets withinOffsets = new RacingLineOffsets();
float leftRacingLineEdge =
-someRacingLineRadius - someOffsetWithinRadius;
withinOfffsets.setSignedDistanceToRacingLine(
RacingLine.eLeftEdge, leftRacingLineEdge);
withinOffsets.setSignedDistanceToRacingLine(
RacingLine.eCenter, -someOffsetWithinRadius);
float rightRacingLineEdge =
someRacingLineRadius - someOffsetWithinRadius;
withinOffsets.setSignedDistanceToRacingLine(
RacingLine.eRightEdge, rightRacingLineEdge);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(withinOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(idealRacingLineOffset, someOffsetWithinRadius);
}
Not DRY

60. #pracunittests
Wet: Helper Functions
void getIdealOffset_WithinRacingLineEdge_ReturnsOffset() {
float someRacingLineRadius = 10.0f;
float someOffsetWithinRadius =
someRacingLineRadius * 0.8f;
!
RacingLineOffsets withinOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetWithinRadius);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(withinOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(
idealRacingLineOffset, someOffsetWithinRadius);
}
void getIdealOffset_BeyondRacingLineEdge_ReturnsEdge() {
float someRacingLineRadius = 10.0f;
float someOffsetBeyondRacingLine =
someRacingLineRadius + 1.0f;
!
RacingLineOffsets beyondOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetBeyondRacingLine);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(beyondOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(
idealRacingLineOffset, withinOffsets.RightEdge);
}

61. #pracunittests
Wet: Helper Functions
void getIdealOffset_WithinRacingLineEdge_ReturnsOffset() {
float someRacingLineRadius = 10.0f;
float someOffsetWithinRadius =
someRacingLineRadius * 0.8f;
!
RacingLineOffsets withinOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetWithinRadius);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(withinOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(
idealRacingLineOffset, someOffsetWithinRadius);
}
void getIdealOffset_BeyondRacingLineEdge_ReturnsEdge() {
float someRacingLineRadius = 10.0f;
float someOffsetBeyondRacingLine =
someRacingLineRadius + 1.0f;
!
RacingLineOffsets beyondOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetBeyondRacingLine);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(beyondOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(
idealRacingLineOffset, withinOffsets.RightEdge);
}

62. #pracunittests
Wet: Helper Functions
void getIdealOffset_WithinRacingLineEdge_ReturnsOffset() {
float someRacingLineRadius = 10.0f;
float someOffsetWithinRadius =
someRacingLineRadius * 0.8f;
!
RacingLineOffsets withinOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetWithinRadius);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(withinOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(
idealRacingLineOffset, someOffsetWithinRadius);
}
void getIdealOffset_BeyondRacingLineEdge_ReturnsEdge() {
float someRacingLineRadius = 10.0f;
float someOffsetBeyondRacingLine =
someRacingLineRadius + 1.0f;
!
RacingLineOffsets beyondOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetBeyondRacingLine);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(beyondOffsets);
!
float idealRacingLineOffset = idealRequest.GetOffset();
TEST_EQUAL(
idealRacingLineOffset, withinOffsets.RightEdge);
}

63. #pracunittests
Wet: Helper Functions
void getIdealOffset_WithinRacingLineEdge_ReturnsOffset() {
float someRacingLineRadius = 10.0f;
float someOffsetWithinRadius =
someRacingLineRadius * 0.8f;
!
RacingLineOffsets withinOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetWithinRadius);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(withinOffsets);
!
test_tauOffsetEqual(idealRequest, someOffsetWithinRadius);
}
void getIdealOffset_BeyondRacingLineEdge_ReturnsEdge() {
float someRacingLineRadius = 10.0f;
float someOffsetBeyondRacingLine =
someRacingLineRadius + 1.0f;
!
RacingLineOffsets beyondOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetBeyondRacingLine);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(beyondOffsets);
!
test_racingLineOffsetEqual(
idealRequest, withinOffsets.RightEdge);
}

64. #pracunittests
Wet: Helper Functions
void getIdealOffset_WithinRacingLineEdge_ReturnsOffset() {
float someRacingLineRadius = 10.0f;
float someOffsetWithinRadius =
someRacingLineRadius * 0.8f;
!
RacingLineOffsets withinOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetWithinRadius);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(withinOffsets);
!
test_tauOffsetEqual(idealRequest, someOffsetWithinRadius);
}
void getIdealOffset_BeyondRacingLineEdge_ReturnsEdge() {
float someRacingLineRadius = 10.0f;
float someOffsetBeyondRacingLine =
someRacingLineRadius + 1.0f;
!
RacingLineOffsets beyondOffsets = CreateRacingLineOffsets(
someRacingLineRadius, someOffsetBeyondRacingLine);
!
OffsetRequest idealRequest =
m_raceBehaviour.getIdealOffset(beyondOffsets);
!
test_racingLineOffsetEqual(
idealRequest, withinOffsets.RightEdge);
}

65. #pracunittests
The Wet Anti-Pattern

66. #pracunittests
The Wet Anti-Pattern
• Hard-to-maintain hacky tests?

67. #pracunittests
The Wet Anti-Pattern
• Hard-to-maintain hacky tests?
• Keep production sensibilities in unit test code

68. #pracunittests
The Wet Anti-Pattern
• Hard-to-maintain hacky tests?
• Keep production sensibilities in unit test code
• Stay DRY with helper functions and custom
asserts

69. #pracunittests
The Wet Anti-Pattern
• Hard-to-maintain hacky tests?
• Keep production sensibilities in unit test code
• Stay DRY with helper functions and custom
asserts
• Do not hide the call to the function under test

70. #pracunittests
3/4: The Deep Anti-Pattern
> Test failed:
> getOwnerAtOffset_WithOwner_ReferencesOwnerAtManyOffsets
> With Assert: VehicleID 0 != 1

71. #pracunittests
void getOwnerAtOffset_WithOwner_ReferencesOwnerAtManyOffsets() {
VehicleID someOwnerID = (VehicleID)1;
LinearDescription ownedDescription =
DefaultFlatLinearDescription().withOwner(someOwnerID);
!
float someNegativeOffset = -1.0f;
float ownerAtNegativeOffset =
ownedDescription.getOwnerAtOffset(someNegativeOffset);
float somePositiveOffset = 1.0f;
float ownerAtPositiveOffset =
ownedDescription.getOwnerAtOffset(somePositiveOffset);
!
test_OwningVehicleIsEqualTo(ownerAtNegativeOffset, someOwnerID);
test_OwningVehicleIsEqualTo(ownerAtPositiveOffset, someOwnerID);
}

72. #pracunittests
void getOwnerAtOffset_WithOwner_ReferencesOwnerAtManyOffsets() {
VehicleID someOwnerID = (VehicleID)1;
LinearDescription ownedDescription =
DefaultFlatLinearDescription().withOwner(someOwnerID);
!
float someNegativeOffset = -1.0f;
float ownerAtNegativeOffset =
ownedDescription.getOwnerAtOffset(someNegativeOffset);
float somePositiveOffset = 1.0f;
float ownerAtPositiveOffset =
ownedDescription.getOwnerAtOffset(somePositiveOffset);
!
test_OwningVehicleIsEqualTo(ownerAtNegativeOffset, someOwnerID);
test_OwningVehicleIsEqualTo(ownerAtPositiveOffset, someOwnerID);
}

73. #pracunittests
void getOwnerAtOffset_WithOwner_ReferencesOwnerAtManyOffsets() {
VehicleID someOwnerID = (VehicleID)1;
LinearDescription ownedDescription =
DefaultFlatLinearDescription().withOwner(someOwnerID);
!
float someNegativeOffset = -1.0f;
float ownerAtNegativeOffset =
ownedDescription.getOwnerAtOffset(someNegativeOffset);
float somePositiveOffset = 1.0f;
float ownerAtPositiveOffset =
ownedDescription.getOwnerAtOffset(somePositiveOffset);
!
test_OwningVehicleIsEqualTo(ownerAtNegativeOffset, someOwnerID);
test_OwningVehicleIsEqualTo(ownerAtPositiveOffset, someOwnerID);
}

74. #pracunittests
void getOwnerAtOffset_WithOwner_ReferencesOwnerAtManyOffsets() {
VehicleID someOwnerID = (VehicleID)1;
LinearDescription ownedDescription =
DefaultFlatLinearDescription().withOwner(someOwnerID);
!
float someNegativeOffset = -1.0f;
float ownerAtNegativeOffset =
ownedDescription.getOwnerAtOffset(someNegativeOffset);
float somePositiveOffset = 1.0f;
float ownerAtPositiveOffset =
ownedDescription.getOwnerAtOffset(somePositiveOffset);
!
test_OwningVehicleIsEqualTo(ownerAtNegativeOffset, someOwnerID);
test_OwningVehicleIsEqualTo(ownerAtPositiveOffset, someOwnerID);
}
>1 explicit
assumption

75. #pracunittests
Deep: One Assert Per Test
void getOwnerAtOffset_WithOwnerAndNegativeOffset_ReturnsOwner() {
float someNegativeOffset = -1.0f;
!
float ownerAtNegativeOffset =
m_ownedDescription.getOwnerAtOffset(someNegativeOffset);
!
test_OwningVehicleIsEqualTo(ownerAtNegativeOffset, m_someOwnerID);
}
!
void getOwnerAtOffset_WithOwnerAndPositiveOffset_ReturnsOwner() {
// *snip*
}

76. #pracunittests
> Test failed:
> getOwnerAtOffset_WithOwnerAndNegativeOffset_ReturnsOwner
> With Assert: VehicleID 0 != 1
> Test failed:
> getOwnerAtOffset_WithOwnerAndPositiveOffset_ReturnsOwner
> With Assert: VehicleID 0 != 1

77. #pracunittests
The Deep Anti-Pattern

78. #pracunittests
The Deep Anti-Pattern
• Test failures not fully informative?

79. #pracunittests
The Deep Anti-Pattern
• Test failures not fully informative?
• Too many explicit assumptions per test

80. #pracunittests
The Deep Anti-Pattern
• Test failures not fully informative?
• Too many explicit assumptions per test
• Minimise assumptions per test

81. #pracunittests
4/4: The Wide Anti-Pattern

82. #pracunittests
4/4: The Wide Anti-Pattern
> Executed 613 test(s), 599 test(s) passed, 14 test(s) failed.

83. #pracunittests
// in DraftBehaviourFixture…
void updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
!
BehaviourSystem behaviourSystem = new BehaviourSystem();
behaviourSystem.addBehaviour(draft);
!
behaviourSystem.updateWithBlackboard(worldInfo);
!
MovementRequest draftMovement = behaviourSystem.getMovementRequest();
TEST_EQUAL(draftMovement.desiredRacingLineOffset, someDraftTargetVehicleOffset);
}

84. #pracunittests
// in DraftBehaviourFixture…
void updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
!
BehaviourSystem behaviourSystem = new BehaviourSystem();
behaviourSystem.addBehaviour(draft);
!
behaviourSystem.updateWithBlackboard(worldInfo);
!
MovementRequest draftMovement = behaviourSystem.getMovementRequest();
TEST_EQUAL(draftMovement.desiredRacingLineOffset, someDraftTargetVehicleOffset);
}

85. #pracunittests
// in DraftBehaviourFixture…
void updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
!
BehaviourSystem behaviourSystem = new BehaviourSystem();
behaviourSystem.addBehaviour(draft);
!
behaviourSystem.updateWithBlackboard(worldInfo);
!
MovementRequest draftMovement = behaviourSystem.getMovementRequest();
TEST_EQUAL(draftMovement.desiredRacingLineOffset, someDraftTargetVehicleOffset);
}

86. #pracunittests
// in DraftBehaviourFixture…
void updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
!
BehaviourSystem behaviourSystem = new BehaviourSystem();
behaviourSystem.addBehaviour(draft);
!
behaviourSystem.updateWithBlackboard(worldInfo);
!
MovementRequest draftMovement = behaviourSystem.getMovementRequest();
TEST_EQUAL(draftMovement.desiredRacingLineOffset, someDraftTargetVehicleOffset);
}
>0 implicit
assumptions

87. #pracunittests
// in DraftBehaviourFixture…
void updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
!
BehaviourSystem behaviourSystem = new BehaviourSystem();
behaviourSystem.addBehaviour(draft);
!
behaviourSystem.updateWithBlackboard(worldInfo);
!
MovementRequest draftMovement = behaviourSystem.getMovementRequest();
TEST_EQUAL(draftMovement.desiredRacingLineOffset, someDraftTargetVehicleOffset);
}

88. #pracunittests
// in DraftBehaviourFixture…
void updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
!
BehaviourSystem behaviourSystem = new BehaviourSystem();
behaviourSystem.addBehaviour(draft);
!
behaviourSystem.updateWithBlackboard(worldInfo);
!
MovementRequest draftMovement = behaviourSystem.getMovementRequest();
TEST_EQUAL(draftMovement.desiredRacingLineOffset, someDraftTargetVehicleOffset);
}

89. #pracunittests
// in DraftBehaviourFixture…
void updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
!
BehaviourSystem behaviourSystem = new BehaviourSystem();
behaviourSystem.addBehaviour(draft);
!
behaviourSystem.updateWithBlackboard(worldInfo);
!
MovementRequest draftMovement = behaviourSystem.getMovementRequest();
TEST_EQUAL(draftMovement.desiredRacingLineOffset, someDraftTargetVehicleOffset);
}

90. #pracunittests
// in DraftBehaviourFixture…
void updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
!
BehaviourSystem behaviourSystem = new BehaviourSystem();
behaviourSystem.addBehaviour(draft);
!
behaviourSystem.updateWithBlackboard(worldInfo);
!
MovementRequest draftMovement = behaviourSystem.getMovementRequest();
TEST_EQUAL(draftMovement.desiredRacingLineOffset, someDraftTargetVehicleOffset);
}

91. #pracunittests
Wide: Seams
void DraftBehaviour.updateImpl(WorldInfo wi, HeatMap heatInOut);
Game Code

92. #pracunittests
Wide: Seams
void DraftBehaviour.updateImpl(WorldInfo wi, HeatMap heatInOut);
class HeatMap { virtual void WriteHeat(float offset, float value) { … } }
Game Code

93. #pracunittests
Wide: Seams
void DraftBehaviour.updateImpl(WorldInfo wi, HeatMap heatInOut);
class HeatMap { virtual void WriteHeat(float offset, float value) { … } }
class MockHeatMap : HeatMap { override void WriteHeat(float offset, float value) { … } }
Game Code
Test Library

94. #pracunittests
Wide: Seams
void DraftBehaviour.updateImpl(WorldInfo wi, HeatMap heatInOut);
class HeatMap { virtual void WriteHeat(float offset, float value) { … } }
class MockHeatMap : HeatMap { override void WriteHeat(float offset, float value) { … } }
Game Code
Test Library

95. #pracunittests
Wide: MockHeatMapvoid updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
MockHeatMap mockMap = new MockHeatMap();
!
draft.updateImpl(worldInfo, mockMap);
!
float draftOffsetWithHighestHeat = mockMap.getHighestHeatOffset();
TEST_EQUAL(draftOffsetWithHighestHeat, someDraftTargetVehicleOffset);
}

96. #pracunittests
Wide: MockHeatMapvoid updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
MockHeatMap mockMap = new MockHeatMap();
!
draft.updateImpl(worldInfo, mockMap);
!
float draftOffsetWithHighestHeat = mockMap.getHighestHeatOffset();
TEST_EQUAL(draftOffsetWithHighestHeat, someDraftTargetVehicleOffset);
}

97. #pracunittests
Wide: MockHeatMapvoid updateImpl_WithCarToDraft_PushesAIToBehindCar() {
WorldInfo worldInfo = new WorldInfo();
float someDraftTargetVehicleOffset = 2.0f;
// *snip* blackboard setup
!
DraftBehaviour draft = new DraftBehaviour();
MockHeatMap mockMap = new MockHeatMap();
!
draft.updateImpl(worldInfo, mockMap);
!
float draftOffsetWithHighestHeat = mockMap.getHighestHeatOffset();
TEST_EQUAL(draftOffsetWithHighestHeat, someDraftTargetVehicleOffset);
}

98. #pracunittests
The Wide Anti-Pattern

99. #pracunittests
The Wide Anti-Pattern
• False-negative test failures?

100. #pracunittests
The Wide Anti-Pattern
• False-negative test failures?
• Many implicit assumptions

101. #pracunittests
The Wide Anti-Pattern
• False-negative test failures?
• Many implicit assumptions
• Isolate code with seams, to enable
simple fake impostors

102. #pracunittests
Recap

103. #pracunittests
Recap
• Respect unit test source code as much as
production source code

104. #pracunittests
Recap
• Respect unit test source code as much as
production source code
• Write once, read many

105. #pracunittests
Recap
• Respect unit test source code as much as
production source code
• Write once, read many
• Only 1 explicit assumption

106. #pracunittests
Recap
• Respect unit test source code as much as
production source code
• Write once, read many
• Only 1 explicit assumption
• Minimise implicit assumptions

107. #pracunittests
• andrew.fray@gmail.com
• @tenpn
• andrewfray.wordpress.com
• Roy Osherove: Art of Unit Testing
www.artofunittesting.com
• Michael Feathers: Working
Effectively with Legacy Code
• Steve Freeman & Nat Pryce:
Growing Object-Orientated
Software, Guided By Tests
Colour scheme by Miaka www.colourlovers.com/palette/444487/Curiosity_Killed