Protocols

The MTKTestable protocol provides an alternative, functional approach to XCTest‘s built in setUp & tearDown methods for handling unit tests.

instanceForTesting() should provide a new instance for each call.

test(_:) should effectively follow this pattern:

static func test(_ testBlock: (Self) -> Void) {

    let testInstance = instanceForTesting()

    // any code that would previously live in setUp

    testBlock(testInstance)

    // any code that would previously live in tearDown

}

With these methods implemented, our test cases now look like this:

func testThings() {

    FooBarClass.test { testInstance in

        XCTAssertNil(testInstance.thingThatShouldBeNil)

    }

}

This allows setUp & tearDown code to exist across multiple files. Moreover, setUp & tearDown logic could now be inherited. As well, MTKTestable protocol extensions could be written to generalize some of the setUp & tearDown logic for large collections of types.