What is the essence of the equivalence class analysis technique?

The equivalence class analysis technique is used to optimize testing by dividing the set of input data into classes, within which the system's behavior is considered the same.

The idea is that instead of testing every possible value, the tester selects one representative from each class, assuming that if the system works correctly with one value from the class, it will work with the others as well.

For example, if a field accepts numbers from 1 to 100, classes can be identified as:

• valid class: 1–100
• invalid classes: less than 1, greater than 100, non-numeric values

Tests select one value from each class, which reduces the number of tests without losing testing quality.