" class="reference-link">TruthTableOption

The TruthTableOption is a Swift protocol which helps both Devs and QAs on writing human-readable and easy editable tests.
It’s applicable anywhere you can synthesize your logic with a Table Of The Truth.

Example and applicable scenario

Imagine a scenario like the following one:
You have to write and test a new feature which tells you whether you need to display a new banner containing a discount code to the users.
You have been told from your business analyst that you only have to show the new banner in your app when:
1) The customer gender is female
2) Is a new customer or is the international women’s day

After discussing with your QAs you end up with the following ACs

newCustomer	isInternationalWomensDay	isFemale	Result
false	false	false	false
false	false	true	false
false	true	false	false
false	true	true	true
true	false	false	false
true	false	true	true
true	true	false	false
true	true	true	true

Developing a feature like that, requires different layers of logic which have to be fully tested.
Pretty sure you’d like to avoid writing single tests for each scenario. Moreover, in future, you should be able to extend this feature
without trying to understand how the logic works.
Debugging gets harder as big as the table and the requirement grows

This can be reduced to something like this:
Screenshot 2020-03-10 at 20 04 03

and here’s where the TruthTableOption comes to rescue.

Usage

Create an enum which has a String as RawValue and conforms to TruthTableOption.
Add a case for each column of the table.
Implement passingScenarios in the following manner:
- For each row where the result is true
  - .true when the condition should be true
  - .false when the condition should be false
  - .dontCare when the condition could be both true or false

enum PromoBanner: String, TruthTableOption {
static var passingScenarios: [Set<TruthTableOptionDescriptor<PromoBanner>>] = [
    [.true(.isFemale), .true(.newCustomer)],
    [.true(.isFemale), .true(.isInternationalWomensDay)],
    [.true(.isFemale), .true(.newCustomer), .true(.isInternationalWomensDay)]
]
    case newCustomer
    case isInternationalWomensDay
    case isFemale
}

Test file

Let’s assume the following mock object

final class PromoBannerMock: PromoBannerInterface {
    var _isNewCustomer: Bool = false
    var _isInternationalWomensDay: Bool = false
    var _isFemale: Bool = false
    var isNewCustomer: Bool {
        return _isNewCustomer
    }
    var isInternationalWomensDay: Bool {
        return _isInternationalWomensDay
    }
    var isFemale: Bool {
        return _isFemale
    }
}

and the following test

func testPromoBanner() {
    // Get the full table of truth and iterate for each row
    for optionRow in PromoBanner.fullOptionTable {
        // Set up the mock object with the current row
        configureState(with: optionRow)
        testScenario(with: optionRow)
    }
}
private func configureState(with optionRow: PromoBanner.Row) {
    promoMock._isNewCustomer = optionRow.contains(.newCustomer)
    promoMock._isInternationalWomensDay = optionRow.contains(.isInternationalWomensDay)
    promoMock._isFemale = optionRow.contains(.isFemale)
}
private func testScenario(with optionRow: MarioBonusLevel.Row) {
    // The result from the manager
    let expectedResult = manager.shouldShowBanner
    // The result from the table of the truth
    let result = optionRow.result
    XCTAssertEqual(result, expectedResult, "Expected result \(expectedResult) instead \(result)")
}

Inspiration

If you are interested in the followed approach, take a look at

License

MIT license