The kata needs random tests.

Test setup is wrong:

main.swift:11:24: error: cannot find 'Dominoes' in scope
        XCTAssertFalse(Dominoes(input).chained)
                       ^~~~~~~~
main.swift:16:24: error: cannot find 'Dominoes' in scope
        XCTAssertFalse(Dominoes(input).chained)
                       ^~~~~~~~
main.swift:21:24: error: cannot find 'Dominoes' in scope
        XCTAssertFalse(Dominoes(input).chained)
                       ^~~~~~~~
main.swift:26:24: error: cannot find 'Dominoes' in scope
        XCTAssertFalse(Dominoes(input).chained)
                       ^~~~~~~~
main.swift:31:24: error: cannot find 'Dominoes' in scope
        XCTAssertFalse(Dominoes(input).chained)
                       ^~~~~~~~
main.swift:36:23: error: cannot find 'Dominoes' in scope
        XCTAssertTrue(Dominoes(input).chained)
                      ^~~~~~~~
main.swift:41:23: error: cannot find 'Dominoes' in scope
        XCTAssertTrue(Dominoes(input).chained)
                      ^~~~~~~~