User interface testing verifies that the interface elements of an application are functioning correctly. When comparing web to mobile applications, one significant difference is the type and variety of user gestures. Mobile apps often require testing for gestures like swiping, pinching, long-presses, etc. Web applications, especially responsive ones, might need testing across different viewport sizes, but the variety of gestures is typically less complex than on mobile. Moreover, mobile app testing may also involve device and OS-specific checks.

Keyboard navigation is a fundamental aspect of accessibility testing because many users, especially those with motor disabilities, might not be able to use a mouse or touch screen effectively. Ensuring that all functionalities of a web application are accessible via keyboard ensures that the app or website is usable by a wider range of users, thereby enhancing its overall accessibility.

Jenkins is a widely-used Continuous Integration/Continuous Deployment tool that facilitates the automation of parts of the development process. By integrating Jenkins with a project's CI/CD pipeline, teams can ensure that automated tests are executed with every build, promoting a robust testing culture in Agile environments.

A "Focus Indicator" is crucial for keyboard navigation, as it visually signifies the current position or element that has focus on a webpage. This is particularly essential for those who rely on the keyboard to navigate, such as individuals with motor disabilities. Without a clear indicator, it would be challenging to understand which part of the webpage is currently active or in focus.

When one of the interacting units isn't fully developed, "Stubs and Drivers" can be employed. A "Stub" is a simplistic implementation of the missing unit, while a "Driver" simulates a unit that calls the incomplete one. These temporary components allow early testing of interactions between units, without waiting for full development.

Exploratory testing, being less structured, allows testers to rapidly identify and react to software behavior. When combined with structured testing, it ensures that not only are predetermined test cases being executed, but the tester's experience, intuition, and creativity also come into play to provide a more comprehensive test coverage. This synergistic combination often results in discovering defects that might have been overlooked with only a structured approach.

Code execution is a dynamic activity where the software is run to check its behavior, whereas reviews are a static technique. Reviews focus on inspecting the product, gathering feedback, and identifying discrepancies without actually running the software.

Setting up automated tests requires a significant initial investment in terms of time, effort, and resources. This includes selecting the right tools, writing the scripts, and maintaining them to adapt to changes in the application being tested.

UI (User Interface) Testing primarily deals with the testing of the visual elements, layouts, and interactive parts of an application. The main goal is to ensure that users have a seamless and consistent visual experience across different functionalities, and that all interactive elements respond as expected.

Network Transition testing focuses on verifying the app's performance and behavior when transitioning between different network conditions, such as moving from WiFi to 4G or experiencing signal drops. It ensures the app remains stable and functional during such changes.