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.

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.

Manual Testing is primarily executed without the intervention of any testing tools. In manual testing, testers execute test cases without using any automation tools. They follow the test steps, input the defined set of data, and compare the actual results with the expected ones, relying solely on human efforts.

Contract Acceptance Testing is performed to validate that the software developed aligns with the requirements specified in the contract between the client and the vendor. This ensures that client expectations and contractual obligations are met.

A bug that was previously fixed but reappears in later phases is typically assigned the status "Reopened." This indicates that the bug was once addressed but has resurfaced, requiring additional attention and potentially a more thorough fix.