The document discusses testing approaches for imperative and functional programming. For imperative programming, tests typically follow the arrange-act-assert pattern and set up object state. For functional programming, tests can be simpler since functions are pure without side effects. Property-based testing with frameworks like QuickCheck and Fox is introduced, which generates random test values rather than writing specific tests. This allows the framework to thoroughly test functions by finding edge cases automatically. An example using Fox to test functions from the Archimedes geometry library in Objective-C is provided.

1. brian gesiak
@modocache
- Born in Greenpoint
- Some of you may know me from the Internet

2. - Quick

3. - Consumers include CapitalOne, GitHub, Artsy, open source projects…

4. brian gesiak
@modocache
- Also iOS Core Systems at Facebook

5. functional programming
in swift
- Excited by interest

6. class Banana {
// ...
func peel() {
peeled = true
}
}
- Still write code like Obj-C, embarrassing

7. imperative programming
- Learn from new field (to me)
- Bring it back to my day job

8. functional programming
imperative programming
- Learn from new field (to me)
- Bring it back to my day job

9. functional programming
imperative programming
- Learn from new field (to me)
- Bring it back to my day job

10. testing
- In particular
- Let’s make sure we’re on same page
- How many people here have written a unit test?

11. why test?
- Confirm app does what you think it does

12. - Imperative tests follow basic pattern
- Set up state, make state change, confirm state change

13. arrange
act
assert
- Imperative tests follow basic pattern
- Set up state, make state change, confirm state change

14. class BananaTests: XCTestCase {
var banana: Banana!
override func setUp() {
// Arrange: Prepare necessary objects, state
banana = Banana(delicious: true)
}
func testPeelRemovesPeel() {
// Act: Perform an action with side effects
banana.peel()
// Assert: Confirm the effects of that action
XCTAssert(banana.peeled)
}
}
- Makes sense with stateful code (explain peel)
- Frameworks like XCTest evolved to help build state

15. class BananaTests: XCTestCase {
var banana: Banana!
override func setUp() {
// Arrange: Prepare necessary objects, state
banana = Banana(delicious: true)
}
func testPeelRemovesPeel() {
// Act: Perform an action with side effects
banana.peel()
// Assert: Confirm the effects of that action
XCTAssert(banana.peeled)
}
}
- Makes sense with stateful code (explain peel)
- Frameworks like XCTest evolved to help build state

16. class BananaTests: XCTestCase {
var banana: Banana!
override func setUp() {
// Arrange: Prepare necessary objects, state
banana = Banana(delicious: true)
}
func testPeelRemovesPeel() {
// Act: Perform an action with side effects
banana.peel()
// Assert: Confirm the effects of that action
XCTAssert(banana.peeled)
}
}
- Makes sense with stateful code (explain peel)
- Frameworks like XCTest evolved to help build state

17. class BananaTests: XCTestCase {
var banana: Banana!
override func setUp() {
// Arrange: Prepare necessary objects, state
banana = Banana(delicious: true)
}
func testPeelRemovesPeel() {
// Act: Perform an action with side effects
banana.peel()
// Assert: Confirm the effects of that action
XCTAssert(banana.peeled)
}
}
- Makes sense with stateful code (explain peel)
- Frameworks like XCTest evolved to help build state

18. beforeEach {
// Arrange #1: Prepare banana
banana = Banana(delicious: true)
}
describe("peel") {
beforeEach {
// Arrange #2: More preparation of banana state
banana.peeled = false
}
it("peels the banana") {
// Act: Perform an action with side effects
banana.peel()
// Assert: Confirm the effects of that action
expect(banana.peeled).to(beTrue())
}
}
- Many frameworks created to build state

19. beforeEach {
// Arrange #1: Prepare banana
banana = Banana(delicious: true)
}
describe("peel") {
beforeEach {
// Arrange #2: More preparation of banana state
banana.peeled = false
}
it("peels the banana") {
// Act: Perform an action with side effects
banana.peel()
// Assert: Confirm the effects of that action
expect(banana.peeled).to(beTrue())
}
}
- Many frameworks created to build state

20. beforeEach {
// Arrange #1: Prepare banana
banana = Banana(delicious: true)
}
describe("peel") {
beforeEach {
// Arrange #2: More preparation of banana state
banana.peeled = false
}
it("peels the banana") {
// Act: Perform an action with side effects
banana.peel()
// Assert: Confirm the effects of that action
expect(banana.peeled).to(beTrue())
}
}
- Many frameworks created to build state

21. beforeEach {
// Arrange #1: Prepare banana
banana = Banana(delicious: true)
}
describe("peel") {
beforeEach {
// Arrange #2: More preparation of banana state
banana.peeled = false
}
it("peels the banana") {
// Act: Perform an action with side effects
banana.peel()
// Assert: Confirm the effects of that action
expect(banana.peeled).to(beTrue())
}
}
- Many frameworks created to build state

22. beforeEach {
// Arrange #1: Prepare banana
banana = Banana(delicious: true)
}
describe("peel") {
beforeEach {
// Arrange #2: More preparation of banana state
banana.peeled = false
}
it("peels the banana") {
// Act: Perform an action with side effects
banana.peel()
// Assert: Confirm the effects of that action
expect(banana.peeled).to(beTrue())
}
}
- Many frameworks created to build state

23. what’s different in functional
programming?
- FP prefers immutable objects and pure functions

24. func peel(banana: Banana) -> PeeledBanana {
return PeeledBanana(delicious: banana.delicious)
}
- Here’s a pure version of peel

25. class PeelTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
// Assert: Peeled banana is equally delicious
let banana = Banana(delicious: false)
let peeledBanana = peel(banana)
XCTAssertFalse(peeledBanana.delicious)
}
}
- FP uses simple data structures, don’t need setup
- Pure functions have no side effects, no act step
- One line

26. class PeelTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
// Assert: Peeled banana is equally delicious
let banana = Banana(delicious: false)
let peeledBanana = peel(banana)
XCTAssertFalse(peeledBanana.delicious)
}
}
- FP uses simple data structures, don’t need setup
- Pure functions have no side effects, no act step
- One line

27. class PeelTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
// Assert: Peeled banana is equally delicious
let banana = Banana(delicious: false)
let peeledBanana = peel(banana)
XCTAssertFalse(peeledBanana.delicious)
}
}
- FP uses simple data structures, don’t need setup
- Pure functions have no side effects, no act step
- One line

28. class PeelTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
// Assert: Peeled banana is equally delicious
let banana = Banana(delicious: false)
let peeledBanana = peel(banana)
XCTAssertFalse(peeledBanana.delicious)
}
}
- FP uses simple data structures, don’t need setup
- Pure functions have no side effects, no act step
- One line

29. functional programming:
spend less time
worrying about state
- That’s the big sell of functional programming

30. xUnit and xSpec
are out of date
- Solving the wrong problem—don’t need setup/teardown
- Haskell has HUnit and hspec, but they’re minor

31. QuickCheck
- Instead, FP focuses on a different problem, solved by QuickCheck

32. class PeelTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
// Assert: Peeled banana is equally delicious
XCTAssertFalse(peel(Banana(delicious: false)).delicious)
XCTAssert(peel(Banana(delicious: true)).delicious)
}
}
- To illustrate look at peel() again
- Tested false, how about true?
- Two params may be OK, but Int?

33. class PeelTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
// Assert: Peeled banana is equally delicious
XCTAssertFalse(peel(Banana(delicious: false)).delicious)
XCTAssert(peel(Banana(delicious: true)).delicious)
}
}
- To illustrate look at peel() again
- Tested false, how about true?
- Two params may be OK, but Int?

34. func testPeelReturnsPeeledBananaWithSameWeight() {
// Test base case
XCTAssertEqual(peel(Banana(weight: 2)).weight, 2)
// Test some edge cases
XCTAssertEqual(peel(Banana(weight: 0)).weight, 0)
XCTAssertEqual(peel(Banana(weight: -1)).weight, -1)
}
- Up to us to determine what to test
- These are example-based tests
- Helps us think about edge cases (but we think of them)

35. func testPeelReturnsPeeledBananaWithSameWeight() {
// Test base case
XCTAssertEqual(peel(Banana(weight: 2)).weight, 2)
// Test some edge cases
XCTAssertEqual(peel(Banana(weight: 0)).weight, 0)
XCTAssertEqual(peel(Banana(weight: -1)).weight, -1)
}
- Up to us to determine what to test
- These are example-based tests
- Helps us think about edge cases (but we think of them)

36. QuickCheck
- Solves this problem
- Basic idea…

37. don’t write tests
generate them
- Fox will throw tons of random data at your function, expecting core properties to hold
- Ported to many languages, and now ObjC and Swift

38. Fox
- Written by Jeff Hui from Pivotal Labs

39. property-based testing
- QuickCheck and Fox are property-based testing frameworks
- What is a property?

40. class BananaTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
let property = forAll(integer()) { weight in
let banana = Banana(weight: weight as Int)
let peeled = peel(banana)
return peeled.weight == banana.weight
}
Fox.Assert(property)
}
}
- Given any integer
- Fox finds the edge cases for us

41. class BananaTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
let property = forAll(integer()) { weight in
let banana = Banana(weight: weight as Int)
let peeled = peel(banana)
return peeled.weight == banana.weight
}
Fox.Assert(property)
}
}
- Given any integer
- Fox finds the edge cases for us

42. class BananaTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
let property = forAll(integer()) { weight in
let banana = Banana(weight: weight as Int)
let peeled = peel(banana)
return peeled.weight == banana.weight
}
Fox.Assert(property)
}
}
- Given any integer
- Fox finds the edge cases for us

43. class BananaTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
let property = forAll(integer()) { weight in
let banana = Banana(weight: weight as Int)
let peeled = peel(banana)
return peeled.weight == banana.weight
}
Fox.Assert(property)
}
}
- Given any integer
- Fox finds the edge cases for us

44. class BananaTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
let property = forAll(integer()) { weight in
let banana = Banana(weight: weight as Int)
let peeled = peel(banana)
return peeled.weight == banana.weight
}
Fox.Assert(property)
}
}
- Given any integer
- Fox finds the edge cases for us

45. class BananaTests: XCTestCase {
func testPeelReturnsPeeledBanana() {
let property = forAll(integer()) { weight in
let banana = Banana(weight: weight as Int)
let peeled = peel(banana)
return peeled.weight == banana.weight
}
Fox.Assert(property)
}
}
- Given any integer
- Fox finds the edge cases for us

46. github/Archimedes
Geometry functions for Cocoa and Cocoa Touch
- Let’s use GitHub’s Archimedes as an example
- It’s ObjC but we can use Fox

47. MEDEdgeInsets insets =
MEDEdgeInsetsMake(10, 5, 10, 5);
- Archimedes defines insets—like padding for a view

48. MEDEdgeInsets insets =
MEDEdgeInsetsMake(10, 5, 10, 5);
10
5 5
10
- Archimedes defines insets—like padding for a view

49. MEDEdgeInsets insets = MEDEdgeInsetsMake(10, 5, 10, 5);
NSString *string = NSStringFromMEDEdgeInsets(insets);
// => @"{10, 5, 10, 5}"
NSString *string = @"{1, 2, 3, 4}";
MEDEdgeInsets insets = MEDEdgeInsetsFromString(string);
// => MEDEdgeInsets(1, 2, 3, 4)
- Contains functions to convert between insets and strings

50. MEDEdgeInsets insets = MEDEdgeInsetsMake(10, 5, 10, 5);
NSString *string = NSStringFromMEDEdgeInsets(insets);
// => @"{10, 5, 10, 5}"
NSString *string = @"{1, 2, 3, 4}";
MEDEdgeInsets insets = MEDEdgeInsetsFromString(string);
// => MEDEdgeInsets(1, 2, 3, 4)
- Contains functions to convert between insets and strings

51. MEDEdgeInsets insets = MEDEdgeInsetsMake(10, 5, 10, 5);
NSString *string = NSStringFromMEDEdgeInsets(insets);
// => @"{10, 5, 10, 5}"
NSString *string = @"{1, 2, 3, 4}";
MEDEdgeInsets insets = MEDEdgeInsetsFromString(string);
// => MEDEdgeInsets(1, 2, 3, 4)
- Contains functions to convert between insets and strings

52. MEDEdgeInsets insets = MEDEdgeInsetsMake(10, 5, 10, 5);
NSString *string = NSStringFromMEDEdgeInsets(insets);
// => @"{10, 5, 10, 5}"
NSString *string = @"{1, 2, 3, 4}";
MEDEdgeInsets insets = MEDEdgeInsetsFromString(string);
// => MEDEdgeInsets(1, 2, 3, 4)
- Contains functions to convert between insets and strings

53. MEDEdgeInsets insets = MEDEdgeInsetsMake(10, 5, 10, 5);
NSString *string = NSStringFromMEDEdgeInsets(insets);
// => @"{10, 5, 10, 5}"
NSString *string = @"{1, 2, 3, 4}";
MEDEdgeInsets insets = MEDEdgeInsetsFromString(string);
// => MEDEdgeInsets(1, 2, 3, 4)
- Contains functions to convert between insets and strings

54. MEDEdgeInsets insets = MEDEdgeInsetsMake(10, 5, 10, 5);
NSString *string = NSStringFromMEDEdgeInsets(insets);
// => @"{10, 5, 10, 5}"
NSString *string = @"{1, 2, 3, 4}";
MEDEdgeInsets insets = MEDEdgeInsetsFromString(string);
// => MEDEdgeInsets(1, 2, 3, 4)
- Contains functions to convert between insets and strings

55. it(@"should create a string from an MEDEdgeInsets", ^{
expect(NSStringFromMEDEdgeInsets(insets)).to(
equal(@"{1, 2, 3, 4}”));
expect(NSStringFromMEDEdgeInsets(insets2)).to(
equal(@"{1.05, 2.05, 3.05, 4.05}”));
});
- Archimedes has example-based tests
- Why 1, 2, 3, 4? No real reason.
- Someone assumed these were good enough

56. it(@"should create a string from an MEDEdgeInsets", ^{
expect(NSStringFromMEDEdgeInsets(insets)).to(
equal(@"{1, 2, 3, 4}”));
expect(NSStringFromMEDEdgeInsets(insets2)).to(
equal(@"{1.05, 2.05, 3.05, 4.05}”));
});
- Archimedes has example-based tests
- Why 1, 2, 3, 4? No real reason.
- Someone assumed these were good enough

57. it(@"should convert between MEDEdgeInsets and strings", ^{
id<FOXGenerator> floats = FOXTuple(
@[FOXFloat(), FOXFloat(), FOXFloat(), FOXFloat()]);
FOXAssert(forAll(floats, ^BOOL(NSArray *generated) {
MEDEdgeInsets insets = MEDEdgeInsetsMake(
[generated[0] floatValue],
[generated[1] floatValue],
[generated[2] floatValue],
[generated[3] floatValue]);
NSString *string = NSStringFromMEDEdgeInsets(insets);
MEDEdgeInsets backToInsets = MEDEdgeInsetsFromString(string);
return MEDEdgeInsetsEqualToEdgeInsets(insets, backToInsets);
}));
});
- Given 4 random numbers, we can convert to string and back

58. it(@"should convert between MEDEdgeInsets and strings", ^{
id<FOXGenerator> floats = FOXTuple(
@[FOXFloat(), FOXFloat(), FOXFloat(), FOXFloat()]);
FOXAssert(forAll(floats, ^BOOL(NSArray *generated) {
MEDEdgeInsets insets = MEDEdgeInsetsMake(
[generated[0] floatValue],
[generated[1] floatValue],
[generated[2] floatValue],
[generated[3] floatValue]);
NSString *string = NSStringFromMEDEdgeInsets(insets);
MEDEdgeInsets backToInsets = MEDEdgeInsetsFromString(string);
return MEDEdgeInsetsEqualToEdgeInsets(insets, backToInsets);
}));
});
- Given 4 random numbers, we can convert to string and back

59. it(@"should convert between MEDEdgeInsets and strings", ^{
id<FOXGenerator> floats = FOXTuple(
@[FOXFloat(), FOXFloat(), FOXFloat(), FOXFloat()]);
FOXAssert(forAll(floats, ^BOOL(NSArray *generated) {
MEDEdgeInsets insets = MEDEdgeInsetsMake(
[generated[0] floatValue],
[generated[1] floatValue],
[generated[2] floatValue],
[generated[3] floatValue]);
NSString *string = NSStringFromMEDEdgeInsets(insets);
MEDEdgeInsets backToInsets = MEDEdgeInsetsFromString(string);
return MEDEdgeInsetsEqualToEdgeInsets(insets, backToInsets);
}));
});
- Given 4 random numbers, we can convert to string and back

60. it(@"should convert between MEDEdgeInsets and strings", ^{
id<FOXGenerator> floats = FOXTuple(
@[FOXFloat(), FOXFloat(), FOXFloat(), FOXFloat()]);
FOXAssert(forAll(floats, ^BOOL(NSArray *generated) {
MEDEdgeInsets insets = MEDEdgeInsetsMake(
[generated[0] floatValue],
[generated[1] floatValue],
[generated[2] floatValue],
[generated[3] floatValue]);
NSString *string = NSStringFromMEDEdgeInsets(insets);
MEDEdgeInsets backToInsets = MEDEdgeInsetsFromString(string);
return MEDEdgeInsetsEqualToEdgeInsets(insets, backToInsets);
}));
});
- Given 4 random numbers, we can convert to string and back

61. it(@"should convert between MEDEdgeInsets and strings", ^{
id<FOXGenerator> floats = FOXTuple(
@[FOXFloat(), FOXFloat(), FOXFloat(), FOXFloat()]);
FOXAssert(forAll(floats, ^BOOL(NSArray *generated) {
MEDEdgeInsets insets = MEDEdgeInsetsMake(
[generated[0] floatValue],
[generated[1] floatValue],
[generated[2] floatValue],
[generated[3] floatValue]);
NSString *string = NSStringFromMEDEdgeInsets(insets);
MEDEdgeInsets backToInsets = MEDEdgeInsetsFromString(string);
return MEDEdgeInsetsEqualToEdgeInsets(insets, backToInsets);
}));
});
- Given 4 random numbers, we can convert to string and back

62. it(@"should convert between MEDEdgeInsets and strings", ^{
id<FOXGenerator> floats = FOXTuple(
@[FOXFloat(), FOXFloat(), FOXFloat(), FOXFloat()]);
FOXAssert(forAll(floats, ^BOOL(NSArray *generated) {
MEDEdgeInsets insets = MEDEdgeInsetsMake(
[generated[0] floatValue],
[generated[1] floatValue],
[generated[2] floatValue],
[generated[3] floatValue]);
NSString *string = NSStringFromMEDEdgeInsets(insets);
MEDEdgeInsets backToInsets = MEDEdgeInsetsFromString(string);
return MEDEdgeInsetsEqualToEdgeInsets(insets, backToInsets);
}));
});
- Given 4 random numbers, we can convert to string and back

63. it(@"should convert between MEDEdgeInsets and strings", ^{
id<FOXGenerator> floats = FOXTuple(
@[FOXFloat(), FOXFloat(), FOXFloat(), FOXFloat()]);
FOXAssert(forAll(floats, ^BOOL(NSArray *generated) {
MEDEdgeInsets insets = MEDEdgeInsetsMake(
[generated[0] floatValue],
[generated[1] floatValue],
[generated[2] floatValue],
[generated[3] floatValue]);
NSString *string = NSStringFromMEDEdgeInsets(insets);
MEDEdgeInsets backToInsets = MEDEdgeInsetsFromString(string);
return MEDEdgeInsetsEqualToEdgeInsets(insets, backToInsets);
}));
});
- Given 4 random numbers, we can convert to string and back

64. MEDEdgeInsets MEDEdgeInsetsFromString(NSString *string) {
int top = 0, left = 0, bottom = 0, right = 0;
sscanf(string.UTF8String,
"{%d, %d, %d, %d}”,
&top, &left, &bottom, &right);
return MEDEdgeInsetsMake((CGFloat)top,
(CGFloat)left
(CGFloat)bottom,
(CGFloat)right);
}
- Let’s say there was a bug in function to convert string to insets

65. MEDEdgeInsets MEDEdgeInsetsFromString(NSString *string) {
int top = 0, left = 0, bottom = 0, right = 0;
sscanf(string.UTF8String,
"{%d, %d, %d, %d}”,
&top, &left, &bottom, &right);
return MEDEdgeInsetsMake((CGFloat)top,
(CGFloat)left
(CGFloat)bottom,
(CGFloat)right);
}
- Let’s say there was a bug in function to convert string to insets

66. {126.0, -299.0, 16.0, 75.0}
- Fox will find a failure
- Then it shrinks to find the smallest failing case

67. {126.0, -299.0, 16.0, 75.0} => {126.0, -299.0, 16.0, 75.0}
- Fox will find a failure
- Then it shrinks to find the smallest failing case

68. {126.0, -299.0, 16.0, 75.0} =>
{9.87, 0.52, -4.21, 26.0} => {9.0, 0.0, -4.0, 26.0}
{126.0, -299.0, 16.0, 75.0}
- Fox will find a failure
- Then it shrinks to find the smallest failing case

69. {126.0, -299.0, 16.0, 75.0} =>
{9.87, 0.52, -4.21, 26.0} => {9.0, 0.0, -4.0, 26.0}
{126.0, -299.0, 16.0, 75.0}
- Fox will find a failure
- Then it shrinks to find the smallest failing case

70. {126.0, -299.0, 16.0, 75.0} =>
{9.87, 0.52, -4.21, 26.0} => {9.0, 0.0, -4.0, 26.0}
{126.0, -299.0, 16.0, 75.0}
{4.93, 0.26, -2.10, 13.0} => {4.0, 0.0, -2.0, 13.0}
- Fox will find a failure
- Then it shrinks to find the smallest failing case

71. {126.0, -299.0, 16.0, 75.0} =>
{9.87, 0.52, -4.21, 26.0} => {9.0, 0.0, -4.0, 26.0}
{126.0, -299.0, 16.0, 75.0}
{4.93, 0.26, -2.10, 13.0} => {4.0, 0.0, -2.0, 13.0}
{2.46, 0.13, -1.05, 6.5} => {-2.0, 0.0, -1.0, 6.0}
- Fox will find a failure
- Then it shrinks to find the smallest failing case

72. {126.0, -299.0, 16.0, 75.0} =>
{9.87, 0.52, -4.21, 26.0} => {9.0, 0.0, -4.0, 26.0}
{126.0, -299.0, 16.0, 75.0}
{4.93, 0.26, -2.10, 13.0} => {4.0, 0.0, -2.0, 13.0}
{2.46, 0.13, -1.05, 6.5} => {-2.0, 0.0, -1.0, 6.0}
...
{0.1, 0.0, 0.0, 0.0} => {0.0, 0.0, 0.0, 0.0}
- Fox will find a failure
- Then it shrinks to find the smallest failing case

73. it(@"should convert between MEDEdgeInsets and strings", ^{
id<FOXGenerator> floats = FOXTuple(
@[FOXFloat(), FOXFloat(), FOXFloat(), FOXFloat()]);
FOXAssert(forAll(floats, ^BOOL(NSArray *generated) {
MEDEdgeInsets insets = MEDEdgeInsetsMake(
[generated[0] floatValue],
[generated[1] floatValue],
[generated[2] floatValue],
[generated[3] floatValue]);
NSString *string = NSStringFromMEDEdgeInsets(insets);
MEDEdgeInsets backToInsets = MEDEdgeInsetsFromString(string);
return MEDEdgeInsetsEqualToEdgeInsets(insets, backToInsets);
}));
});
- So when you run the test, it’s easier to interpret failure
- Property-based tests are powerful
- Can use in tandem with example-based tests

74. it(@"should convert between MEDEdgeInsets and strings", ^{
id<FOXGenerator> floats = FOXTuple(
@[FOXFloat(), FOXFloat(), FOXFloat(), FOXFloat()]);
FOXAssert(forAll(floats, ^BOOL(NSArray *generated) {
MEDEdgeInsets insets = MEDEdgeInsetsMake(
Property failed with (0.1, 0.0, 0.0, 0.0)
[generated[0] floatValue],
[generated[1] floatValue],
[generated[2] floatValue],
[generated[3] floatValue]);
NSString *string = NSStringFromMEDEdgeInsets(insets);
MEDEdgeInsets backToInsets = MEDEdgeInsetsFromString(string);
return MEDEdgeInsetsEqualToEdgeInsets(insets, backToInsets);
}));
});
- So when you run the test, it’s easier to interpret failure
- Property-based tests are powerful
- Can use in tandem with example-based tests

75. test stateful code
- Not only can be used together with example-based tests
- Can also test stateful things like view controllers

76. - We can use Fox

77. - We can use Fox

78. state
- Model changes in state using transitions
- Transitions have corresponding “model state” updates
- Specify conditions that must be met after transition

79. state
more transition
less transition
- Model changes in state using transitions
- Transitions have corresponding “model state” updates
- Specify conditions that must be met after transition

80. state
count
more transition
count + 1
less transition
count - 1
- Model changes in state using transitions
- Transitions have corresponding “model state” updates
- Specify conditions that must be met after transition

81. state
count
property
more transition
count + 1
property
less transition
count - 1
- Model changes in state using transitions
- Transitions have corresponding “model state” updates
- Specify conditions that must be met after transition

82. initial
count = 0
- Fox will run transitions at random, checking that properties hold

83. initial
count = 0
more
count = 1
property
less
count = 0
property
- Fox will run transitions at random, checking that properties hold

84. initial
count = 0
more
count = 1
property
less
count = 0
property
more
count = 1
more
count = 2
- Fox will run transitions at random, checking that properties hold

85. let moreTransition = FOXTransition(action: { state, _ in
let controller = state as BananaViewController
controller.moreButton.sendActionsForControlEvents(
UIControlEvents.TouchUpInside)
}, nextModelState: { modelState, _ in
return (modelState as Int) + 1
})
- Fox gives us a hook to move into the next state
- And we need to update our model state as well

86. let moreTransition = FOXTransition(action: { state, _ in
let controller = state as BananaViewController
controller.moreButton.sendActionsForControlEvents(
UIControlEvents.TouchUpInside)
}, nextModelState: { modelState, _ in
return (modelState as Int) + 1
})
- Fox gives us a hook to move into the next state
- And we need to update our model state as well

87. let moreTransition = FOXTransition(action: { state, _ in
let controller = state as BananaViewController
controller.moreButton.sendActionsForControlEvents(
UIControlEvents.TouchUpInside)
}, nextModelState: { modelState, _ in
return (modelState as Int) + 1
})
- Fox gives us a hook to move into the next state
- And we need to update our model state as well

88. let moreTransition = FOXTransition(action: { state, _ in
let controller = state as BananaViewController
controller.moreButton.sendActionsForControlEvents(
UIControlEvents.TouchUpInside)
}, nextModelState: { modelState, _ in
return (modelState as Int) + 1
})
- Fox gives us a hook to move into the next state
- And we need to update our model state as well

89. let moreTransition = FOXTransition(action: { state, _ in
let controller = state as BananaViewController
controller.moreButton.sendActionsForControlEvents(
UIControlEvents.TouchUpInside)
}, nextModelState: { modelState, _ in
return (modelState as Int) + 1
})
- Fox gives us a hook to move into the next state
- And we need to update our model state as well

90. let moreTransition = FOXTransition(action: { state, _ in
let controller = state as BananaViewController
controller.moreButton.sendActionsForControlEvents(
UIControlEvents.TouchUpInside)
}, nextModelState: { modelState, _ in
return (modelState as Int) + 1
})
- Fox gives us a hook to move into the next state
- And we need to update our model state as well

91. moreTransition.postcondition = { (modelState, _,
subject, _, _) in
let controller = subject as BananaViewController
return modelState as Int == controller.bananaCount
}
- Post condition (or property) is must be fulfilled after every transition—that view controller displays correct model state
- We can only tap more when count < 10

92. moreTransition.postcondition = { (modelState, _,
subject, _, _) in
let controller = subject as BananaViewController
return modelState as Int == controller.bananaCount
}
- Post condition (or property) is must be fulfilled after every transition—that view controller displays correct model state
- We can only tap more when count < 10

93. moreTransition.postcondition = { (modelState, _,
subject, _, _) in
let controller = subject as BananaViewController
return modelState as Int == controller.bananaCount
}
- Post condition (or property) is must be fulfilled after every transition—that view controller displays correct model state
- We can only tap more when count < 10

94. moreTransition.postcondition = { (modelState, _,
subject, _, _) in
let controller = subject as BananaViewController
return modelState as Int == controller.bananaCount
}
moreTransition.precondition = { modelState in
return (modelState as Int) < 10
}
- Post condition (or property) is must be fulfilled after every transition—that view controller displays correct model state
- We can only tap more when count < 10

95. moreTransition.postcondition = { (modelState, _,
subject, _, _) in
let controller = subject as BananaViewController
return modelState as Int == controller.bananaCount
}
moreTransition.precondition = { modelState in
return (modelState as Int) < 10
}
- Post condition (or property) is must be fulfilled after every transition—that view controller displays correct model state
- We can only tap more when count < 10

96. let stateMachine = FOXFiniteStateMachine(
initialModelState: 0)
stateMachine.addTransition(moreTransition)
stateMachine.addTransition(lessTransition)
let executedCommands = executeCommands(stateMachine) {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let controller =
storyboard.instantiateInitialViewController()
as BananaViewController
let _ = controller.view
return controller
}
Fox.Assert(forAll(executedCommands) { commands in
return executedSuccessfully(commands as NSArray)
})
- Same gist for less transition
- Define state machine with initial model state
- Provide initial state with executeCommands
- Minimum failing case displayed

97. let stateMachine = FOXFiniteStateMachine(
initialModelState: 0)
stateMachine.addTransition(moreTransition)
stateMachine.addTransition(lessTransition)
let executedCommands = executeCommands(stateMachine) {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let controller =
storyboard.instantiateInitialViewController()
as BananaViewController
let _ = controller.view
return controller
}
Fox.Assert(forAll(executedCommands) { commands in
return executedSuccessfully(commands as NSArray)
})
- Same gist for less transition
- Define state machine with initial model state
- Provide initial state with executeCommands
- Minimum failing case displayed

98. let stateMachine = FOXFiniteStateMachine(
initialModelState: 0)
stateMachine.addTransition(moreTransition)
stateMachine.addTransition(lessTransition)
let executedCommands = executeCommands(stateMachine) {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let controller =
storyboard.instantiateInitialViewController()
as BananaViewController
let _ = controller.view
return controller
}
Fox.Assert(forAll(executedCommands) { commands in
return executedSuccessfully(commands as NSArray)
})
- Same gist for less transition
- Define state machine with initial model state
- Provide initial state with executeCommands
- Minimum failing case displayed

99. let stateMachine = FOXFiniteStateMachine(
initialModelState: 0)
stateMachine.addTransition(moreTransition)
stateMachine.addTransition(lessTransition)
let executedCommands = executeCommands(stateMachine) {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let controller =
storyboard.instantiateInitialViewController()
as BananaViewController
let _ = controller.view
return controller
}
Fox.Assert(forAll(executedCommands) { commands in
return executedSuccessfully(commands as NSArray)
})
- Same gist for less transition
- Define state machine with initial model state
- Provide initial state with executeCommands
- Minimum failing case displayed

100. let stateMachine = FOXFiniteStateMachine(
initialModelState: 0)
stateMachine.addTransition(moreTransition)
stateMachine.addTransition(lessTransition)
let executedCommands = executeCommands(stateMachine) {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let controller =
storyboard.instantiateInitialViewController()
as BananaViewController
let _ = controller.view
return controller
}
Fox.Assert(forAll(executedCommands) { commands in
return executedSuccessfully(commands as NSArray)
})
- Same gist for less transition
- Define state machine with initial model state
- Provide initial state with executeCommands
- Minimum failing case displayed

101. github.com/jeffh/Fox
fox-testing.readthedocs.org/
- That’s Fox in a nutshell; Many more features, see GitHub
- Property-based testing is deep, many resources available
- Fox will continue to grow, perhaps provide properties

102. functional programming
imperative programming
- QuickCheck has been around since 1999, only in ObjC/Swift recently
- Great example of cross-pollination of ideas, excited for more

103. brian gesiak
@modocache
- Thanks for listening. Questions?