Application testing with Twilio can help simplify maintenance by using various types of tests, including unit testing, error detection, integration testing, and live testing. Unit testing involves writing automated tests to ensure individual units of code behave as intended, while error detection uses tools like Twilio Test Credentials and Error Logs to identify issues before running full end-to-end tests. Integration testing focuses on simulating production traffic to test the entire application, while live testing is designed to help identify outages before customers do, particularly in use cases with irregular usage patterns or low volume traffic. By implementing these types of tests, developers can ensure their Twilio applications are reliable and performant.