Boundary Value Analysis

Boundary Value Analysis (BVA) is a software testing technique that focuses on the boundaries of input values to identify potential defects. This method is particularly useful for testing the limits of input ranges, where errors are most likely to occur. BVA is a subset of Equivalence Partitioning, which divides input data into partitions that can be considered the same. However, BVA specifically targets the values at the edges of these partitions.

Key Concepts

1. Boundary Values
2. Valid and Invalid Boundaries
3. Min, Max, Just Inside, and Just Outside
4. Application in Testing

1. Boundary Values

Boundary Values are the specific values that lie at the edges of input ranges. These values are critical because they are where errors are most likely to occur. For example, if an input range is from 1 to 100, the boundary values would be 1 and 100.

2. Valid and Invalid Boundaries

Valid Boundaries are the values that lie within the acceptable range of input values. Invalid Boundaries are the values that lie just outside the acceptable range. For instance, if the valid range is 1 to 100, the valid boundaries are 1 and 100, while the invalid boundaries are 0 and 101.

3. Min, Max, Just Inside, and Just Outside

In BVA, testers often consider four key values around each boundary:

• Min: The smallest value within the valid range (e.g., 1).
• Max: The largest value within the valid range (e.g., 100).
• Just Inside: The value immediately inside the boundary (e.g., 2 for the lower boundary and 99 for the upper boundary).
• Just Outside: The value immediately outside the boundary (e.g., 0 for the lower boundary and 101 for the upper boundary).

4. Application in Testing

BVA is applied by designing test cases that include these boundary values. This ensures that the software behaves correctly at the limits of its input ranges. For example, if a function accepts an integer between 1 and 100, the test cases would include:

        Test Case 1: Input = 1 (Min)
        Test Case 2: Input = 100 (Max)
        Test Case 3: Input = 2 (Just Inside Min)
        Test Case 4: Input = 99 (Just Inside Max)
        Test Case 5: Input = 0 (Just Outside Min)
        Test Case 6: Input = 101 (Just Outside Max)
    

By focusing on these boundary values, testers can identify defects that might not be caught by testing random values within the range. This method is particularly effective in finding issues related to input validation and error handling.

For instance, consider a function that calculates the discount based on the number of items purchased. The discount rules are as follows:

• No discount for 0 items.
• 10% discount for 1 to 10 items.
• 20% discount for 11 to 20 items.
• 30% discount for 21 or more items.

Using BVA, the test cases would include:

        Test Case 1: Items = 0 (Just Outside Min of 1st Range)
        Test Case 2: Items = 1 (Min of 1st Range)
        Test Case 3: Items = 10 (Max of 1st Range)
        Test Case 4: Items = 11 (Min of 2nd Range)
        Test Case 5: Items = 20 (Max of 2nd Range)
        Test Case 6: Items = 21 (Min of 3rd Range)
    

By testing these boundary values, testers can ensure that the discount calculation is correct at the edges of each range, where errors are most likely to occur.