class SystemTest {

    // Test Double
    class AuthorizerDummy: Authorizer {
        func authorize(username: String, password: String) -> Bool {
            return true
        }
    }

    func testAuthorizedUserIsNilWhenInit() {
        // Given
        let dummy = AuthorizerDummy()

        // When
        let sut = System(with: dummy)

        // Then
        assert(sut.authorizedUser == nil)
    }
}