https://github.com/krzysztofzablocki/difference

Simple way to identify what is different between 2 instances of any type. Must have for TDD.
https://github.com/krzysztofzablocki/difference

ios macos swift testing tvos watchos

Last synced: 6 days ago
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Simple way to identify what is different between 2 instances of any type. Must have for TDD.

• Host: GitHub
• URL: https://github.com/krzysztofzablocki/difference
• Owner: krzysztofzablocki
• License: mit
• Created: 2017-10-18T13:01:12.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2024-08-05T13:34:30.000Z (6 months ago)
• Last Synced: 2025-01-09T07:04:17.391Z (13 days ago)
• Topics: ios, macos, swift, testing, tvos, watchos
• Language: Swift
• Homepage: http://merowing.info
• Size: 2.63 MB
• Stars: 1,220
• Watchers: 13
• Forks: 54
• Open Issues: 4
• Metadata Files:
  • Readme: README.md
  • Funding: .github/FUNDING.yml
  • License: LICENSE

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# Difference

Better way to identify what's different between 2 instances.

Have you ever written tests? 

Usually they use equality asserts, e.g. `XCTAssertEqual`, what happens if the objects aren't equal? Xcode throws a wall of text at you:

![](Resources/before.png)

This forces you to manually scan the text and try to figure out exactly what's wrong, what if instead you could just learn which property is different?

![](Resources/after.png)

[**If you'd like to support my work and improve your engineering workflows, check out my SwiftyStack course**](https://www.swiftystack.com/)

## Installation

### CocoaPods

Add `pod 'Difference'` to your Podfile.

### Carthage

Add `github "krzysztofzablocki/Difference"` to your Cartfile.

### SwiftPM

Add `.package(url: "https://github.com/krzysztofzablocki/Difference.git", branch: "master")` dependency in your Package manifest.

## Using lldb

Write the following to see the difference between 2 instances:

`po dumpDiff(expected, received)`

## Integrate with XCTest

Add this to your test target:

```swift

public func XCTAssertEqual(_ expected: @autoclosure () throws -> T, _ received: @autoclosure () throws -> T, file: StaticString = #filePath, line: UInt = #line) {

    do {

        let expected = try expected()

        let received = try received()

        XCTAssertTrue(expected == received, "Found difference for \n" + diff(expected, received).joined(separator: ", "), file: file, line: line)

    }

    catch {

        XCTFail("Caught error while testing: \(error)", file: file, line: line)

    }

}

```

Replace `#filePath` with `#file` if you're using Xcode 11 or earlier.

## Integrate with Quick

Add this to your test target:

```swift

public func equalDiff(_ expectedValue: T?) -> Predicate {

    return Predicate.define { actualExpression in

        let receivedValue = try actualExpression.evaluate()

        if receivedValue == nil {

            var message = ExpectationMessage.fail("")

            if let expectedValue = expectedValue {

                message = ExpectationMessage.expectedCustomValueTo("equal <\(expectedValue)>", actual: "nil")

            }

            return PredicateResult(status: .fail, message: message)

        }

        if expectedValue == nil {

            return PredicateResult(status: .fail, message: ExpectationMessage.fail("").appendedBeNilHint())

        }

        return PredicateResult(bool: receivedValue == expectedValue, message: ExpectationMessage.fail("Found difference for " + diff(expectedValue, receivedValue).joined(separator: ", ")))

    }

}

```

Write the following to see the difference between 2 instances:

`expect(received).to(equalDiff(expected))`

## Integrate with The Composable Architecture

If you are using The Composable Architecture `nameLabels` configuration to get a diff that's more appropiate for reducer instrumentation

```swift

diff(oldState, newState, indentationType: .pipe, nameLabels: .comparing)

```

You can use this function in your own variant of [ReducerInstrumentation code based on this](https://github.com/pointfreeco/swift-composable-architecture/blob/e7dda73c35f1016c8ba82fd2b7c43757cce68e58/Sources/ComposableArchitecture/Debugging/ReducerDebugging.swift)

That way your diffs will look more like this:

```swift

Received action:

  AppAction.home(.howTo(.setSelectedSlide))

State:

home:

|	selectedHowTo:

|	|	selectedSlide:

|	|	|	Current: 8mnkni91h4fe

|	|	|	Previous: exei4wpqsmdk

```