Overview
Boundary value analysis (BVA) and equivalence partitioning (EP) are both black box test design techniques used in manual testing. BVA is considered more effective in certain scenarios, especially when testing the edge cases of input domains. This technique helps in identifying errors at the boundaries rather than within the ranges of input, where equivalence partitioning typically focuses.
Key Concepts
- Boundary Value Analysis (BVA): Focuses on testing at the boundaries between partitions. It's based on the principle that bugs are more frequent at the edges of input ranges.
- Equivalence Partitioning (EP): Divides input data into partitions of equivalent data from which test cases can be derived. It aims to reduce the total number of test cases to a manageable level, while still covering all possible scenarios.
- Edge Case Testing: Particularly important in scenarios where system behavior could change dramatically at the boundary values. BVA is instrumental in this context.
Common Interview Questions
Basic Level
- What is boundary value analysis?
- How does equivalence partitioning differ from boundary value analysis?
Intermediate Level
- Why is boundary value analysis considered more effective for edge case testing than equivalence partitioning?
Advanced Level
- Can you provide an example scenario where boundary value analysis would significantly outperform equivalence partitioning in identifying defects?
Detailed Answers
1. What is boundary value analysis?
Answer: Boundary Value Analysis (BVA) is a testing technique that focuses on the values at the edge of equivalence partitions. It is based on the theory that errors are most prevalent at the boundaries of input domains. When applying BVA, test cases are designed to include values at the boundaries, as well as just inside and just outside of each partition.
Key Points:
- BVA helps in identifying defects that are not apparent within the typical range of input values.
- It is particularly effective in scenarios where an application's response might differ at the edge of an input range.
- This technique can be applied to a variety of test levels, including unit, integration, and system testing.
Example:
Assuming a scenario where an application accepts an integer value between 1 and 100 inclusive:
public bool IsValidNumber(int number)
{
return number >= 1 && number <= 100;
}
Test cases based on BVA would include testing with values 0, 1, 100, and 101 to cover the boundary conditions and just outside/inside of the valid range.
2. How does equivalence partitioning differ from boundary value analysis?
Answer: While both are testing techniques used to reduce the number of test cases and ensure wide coverage, Equivalence Partitioning (EP) divides the input data into partitions of equivalent data, and only one condition from each partition is tested. In contrast, Boundary Value Analysis (BVA) focuses on creating test cases for values at the edges of these partitions.
Key Points:
- EP is used to minimize the total number of test cases by treating similar values equivalently.
- BVA complements EP by ensuring that the edges of these partitions are thoroughly tested.
- EP and BVA are often used together to achieve both broad and deep test coverage.
Example:
Using the same validation method from the previous example, an equivalence partitioning approach would involve testing with values like:
- A value in the valid range (e.g., 50)
- A value below the valid range (e.g., 0)
- A value above the valid range (e.g., 101)
3. Why is boundary value analysis considered more effective for edge case testing than equivalence partitioning?
Answer: Boundary Value Analysis is considered more effective for edge case testing because it directly targets the areas where software behavior tends to be most erratic: at the boundaries of input ranges. While equivalence partitioning assumes that all values within a partition will be treated the same by the software, BVA acknowledges that edge cases often behave differently and thus require explicit testing.
Key Points:
- Edge cases are more prone to errors and may not behave as expected, making BVA a crucial technique.
- BVA can uncover defects that are missed by EP, as EP might not include test cases for boundary values.
- Implementing BVA can significantly improve the robustness of software testing, especially in critical applications.
4. Can you provide an example scenario where boundary value analysis would significantly outperform equivalence partitioning in identifying defects?
Answer: Consider an application that calculates bonuses for sales between $500 and $1000, inclusive, where the calculation logic changes at the boundary values. Equivalence partitioning might test one value within the valid range and one value outside, potentially missing boundary-specific defects.
Key Points:
- The logic for calculating bonuses might have defects at the exact values of $500 and $1000.
- By focusing on these boundary values, BVA directly targets potential defect areas that EP might overlook.
- BVA is thus essential for thoroughly testing the functionality and ensuring accurate bonus calculations.
Example:
public decimal CalculateBonus(decimal salesAmount)
{
if (salesAmount < 500 || salesAmount > 1000)
return 0;
else if (salesAmount == 500)
return 50; // Special bonus logic at lower boundary
else
return (salesAmount - 500) * 0.1m; // General bonus calculation
}
Boundary value analysis would prompt testing at $499, $500, $1000, and $1001, ensuring the special logic and general calculation are both correct, whereas equivalence partitioning might miss the special bonus logic at the boundaries.
