Boundary Value Analysis (BVA) and Equivalence Partitioning (EP) are black-box software testing techniques used to reduce the number of test cases required while maximizing test coverage, especially when dealing with a range of input values. 

This is where effective test case design techniques become essential. Rather than testing every possible input combination, we need strategic approaches that maximize our testing coverage while minimizing effort and time. Two major techniques that address this challenge are Boundary Value Analysis (BVA) and Equivalence Partitioning (EP).

These techniques help testers create comprehensive test suites that are both efficient and effective, ensuring thorough coverage without the burden of exhaustive testing.

Boundary Value Analysis (BVA)

Definition

Boundary Value Analysis is a test case design technique that focuses specifically on input values at boundary conditions. The fundamental principle behind BVA is that boundaries represent critical points where software applications are most likely to fail. By concentrating testing efforts on these boundary values, testers can identify defects that might otherwise go unnoticed.

Key Concept

The core concept of BVA is based on the observation that errors are most likely to occur at the upper and lower limits of input ranges. Software systems often handle values within normal ranges correctly but fail when processing values at the extremes of acceptable input ranges or just outside those ranges.

Example 1: Age Range (20–50)

Let's consider a system that accepts age values between 20 and 50. Using BVA, we would design the following test cases:

Invalid test cases:

• 19 (min-1): One value below the minimum acceptable range
• 51 (max+1): One value above the maximum acceptable range

Valid test cases:

• 20 (min): The minimum boundary value
• 21 (min+1): One value above the minimum boundary
• 30 (nominal): A value within the normal range
• 49 (max-1): One value below the maximum boundary
• 50 (max): The maximum boundary value

Example 2: Age Range (18–56)

For a different system accepting ages between 18 and 56, our BVA test cases would be:

Invalid test cases:

• 17 (min-1): Below the minimum range
• 57 (max+1): Above the maximum range

Valid test cases:

• 18: Minimum boundary
• 19: Just above minimum
• 37: Nominal value
• 55: Just below maximum
• 56: Maximum boundary

Equivalence Partitioning (EP)

Definition

Equivalence Partitioning, also known as Equivalence Class Partitioning (ECP), is a black-box testing technique that divides all possible inputs into distinct classes or groups. Each group represents a set of inputs that should theoretically produce similar behavior from the system under test.

Key Concept

The fundamental principle of EP is that selecting one representative value from each equivalence class is sufficient for testing purposes. If one value from a particular class works correctly, all other values in the same class are expected to behave similarly. This approach significantly reduces the number of test cases needed while maintaining comprehensive coverage.

Comparison: BVA vs EP

Technique

The primary difference in approach between these two techniques lies in their focus areas:

• BVA: Concentrates specifically on boundary conditions and edge cases
• EP: Focuses on selecting representative values from distinct input classes

Test Values

The selection of test values differs significantly between the two approaches:

• BVA: Uses a systematic approach with min-1, min, min+1, nominal, max-1, max, and max+1 values
• EP: Chooses one representative value from each valid and invalid equivalence class

Purpose

Each technique serves a distinct purpose in the testing strategy:

• BVA: Specifically designed to detect errors that occur at boundary conditions
• EP: Aims to reduce the total number of test cases while ensuring adequate coverage across all input categories

Conclusion

Both Boundary Value Analysis and Equivalence Partitioning are essential test case design techniques that serve complementary purposes in software testing. BVA ensures the detection of edge-case errors that commonly occur at input boundaries, while EP optimizes testing effort through representative sampling of input classes.

When used together, these techniques significantly improve both the efficiency and effectiveness of software testing. They provide a structured approach to test case design that maximizes defect detection while minimizing the resources required for comprehensive testing coverage.