What does boundary value analysis focus on when testing?

Boundary value analysis is a testing technique that is particularly focused on identifying errors at the extreme ends or boundaries of input ranges. This approach is grounded in the observation that errors are more likely to occur at the boundaries than in the middle of input ranges. In this context, testing involves selecting values that are exactly at, just below, and just above the boundaries, allowing testers to effectively uncover potential defects that might not be evident through other testing methods.

By concentrating on these boundary values, the technique helps in verifying that the application behaves correctly at critical points of input. For instance, if an input field accepts values from 1 to 100, boundary value analysis would involve testing the values 1, 100, 0 (just below the lower boundary), and 101 (just above the upper boundary). This method provides a more rigorous examination of the software under test and increases the likelihood of detecting bugs that may otherwise go unnoticed in the center of value ranges.

In contrast, the other options do not capture the primary focus of boundary value analysis. Testing values outside input ranges, testing midpoint values, or testing random values fails to specifically address the crucial aspect of boundary conditions, which is the essence of this testing technique.