Boundary value problem: age field from 18 to 25 inclusive. Minimum number of checks?

To test the age field with a restriction from 18 to 25 inclusive, the minimum number of tests can be reduced to three:

1. Check the value at the lower boundary (18) — it should pass.
2. Check the value at the upper boundary (25) — it should pass.
3. Check a value outside the range (for example, 17 or 26) — it should not pass.

Thus, we test the boundary values and at least one value outside the range to ensure that validation works correctly.