What is the starting point of the bottom-up approach to software testing?

The bottom-up approach to software testing begins with the testing of atomic units, such as individual modules or components of the software. This method focuses on verifying the functionality and performance of the smallest parts of the application before integrating them with larger systems.

By starting with these atomic units, testers can identify and resolve defects at a granular level. This ultimately helps in ensuring that the building blocks of the software are functioning correctly before moving on to more complex interactions in higher-level testing stages. As the testing progresses, modules are integrated, and additional layers of testing, such as integration testing, system testing, and acceptance testing, are conducted. This staged testing process helps in building confidence in the software's reliability and performance progressively.

While system integration testing, user acceptance testing, and documentation verification are important aspects of the software development lifecycle, they do not represent the foundation of the bottom-up approach. Instead, they occur later in the testing process once the atomic units have been validated.