How many checks need to be performed when analyzing boundary values?

To analyze boundary values, at least three checks are required for each boundary condition:

1. On the boundary: The value is exactly on the boundary of the range.
2. Near the boundary (inside the range): The value minimally differs from the boundary but is within the permissible range.
3. Near the boundary (outside the range): The value minimally differs from the boundary but is outside the permissible range.

Example for a numeric field with a range from 1 to 10:

• 1 (at the lower boundary)
• 2 (close to the lower boundary, inside)
• 0 (close to the lower boundary, outside)
• 10 (at the upper boundary)
• 9 (close to the upper boundary, inside)
• 11 (close to the upper boundary, outside)

For logical or string boundaries (e.g., minimum/maximum string length), the principle remains the same: tests at the boundary itself, slightly less, and slightly more.