To build an iOS application, you must employ Apple's macOS hardware, adhere to Apple's licensing requirements, and leverage XCODE software, which requires a significant initial investment in creating an in-house build-and-test pipeline or outsourcing it to external cloud vendors. Conducting UI testing on iOS applications using XCUITest is essential, as it provides developers with better reliability due to its seamless integration with Xcode and ability to interact with UI elements. Leveraging Sauce Labs helps address challenges by providing cost-effective testing, scalability, faster feedback cycles, extensive device and OS coverage, hassle-free maintenance, and seamless collaboration. With Sauce Labs, you can now run XCUITests on simulators as well as real devices, allowing for quick and easy testing across various devices and configurations.