How to test an interval using the boundary value method?

To test the interval [a, b] using the boundary value method, the following points are checked:

• a: the lower boundary of the interval.
• a + 1: a value slightly greater than the lower boundary.
• b: the upper boundary of the interval.
• b - 1: a value slightly less than the upper boundary.
• A value outside the interval on the right (greater than b).
• A value outside the interval on the left (less than a).

Additionally, if applicable, consider:

• The midpoint of the interval (a + b) / 2.
• Boundary values for data types (e.g., maximum/minimum int).
• Special boundary cases if known from requirements (e.g., 0, -1, 1).

For example, for the interval [10, 100]:

• 10
• 11
• 100
• 99
• 101
• 9
• 55 (midpoint)

If an open or half-open interval is used, the methodology is adjusted accordingly. For example, for the interval (a, b), check a+1, b-1, a, b, and values outside the interval.