How to write performance tests using measure()

Swift version: 5.6

Paul Hudson    @twostraws    May 28th 2019

Performance tests let you check how fast your code runs, but more importantly it lets you check how fast your code runs over time – you can spot performance changes as your code evolves.

Writing a performance test takes just two steps:

1. Create a new method starting with the name “test” in your Xcode tests.
2. Using the measure() method inside that test, running any work you want.

To try it out, look in the “Tests” group in your Xcode project, then open your tests file. In my test I’m going to try generating images using a fictional ImageGenerator struct that has a generateImages() method. I’m specifically going to be testing the generateImages() method, which means I’ll create a test instance of ImageGenerator outside the measure() method, like this:

func testPerformanceExample() {
    let generator = ImageGenerator()

    measure {
        generator.generateImages()
    }
}

When that test runs, Xcode will run the contents of measure() 10 times to get a spread of results.

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