Black Box Testing Techniques : Equivalence Partitioning

In previous articles we learned about Testing Techniques Overview and then Specification Based Testing Techniques or Black Box testing techniques overview.

Specification Based Testing Techniques(click here to read)

• Boundary Value Analysis
• Decision Table Testing
• State Transition Testing 
• Use Case Testing
• Cause-effect graph
• Classification tree method
• Domain Analysis

 In this article we will learn about Test Designing Technique 

Equivalence Partitioning

“A black box test design technique in which test cases are designed to execute representatives from equivalence partitions. In principle test cases are designed to cover each partition at least once.” [ISTQB glossary]


If you expect the same result from two tests, you consider them equivalent. A group of tests forms a class if you believe that:

• They all test the same thing
• If one test catches a bug, the others probably will too
• If one test doesn’t catch a bug, the others probably won’t either 

The following is assumed true about EP: 

• If one value in an equivalence partition finds a defect, any value in the same equivalence partition will likely to find the same defect. 
• If one value in an equivalence partition does not find a defect, no other value in the same equivalence partition is likely to find a defect.

When to use: 

• Systems in which much of the input data takes on values within ranges or within sets. Data sets are partitioned based on common attributes rather than minimum and maximum.

Example:

• International flights can take place between capital cities only.
• Non-capital cities can be selected for domestic flights. It can be applied at any level of testing.

Examples:

• Date control testing at component testing
• Testing customer orders at system testing 

Identifying Equivalence classes:

Here are a few guidelines for identifying equivalence classes:

• Look for ranges of numbers
• Don’t forget equivalence classes for invalid inputs
• Analyze responses to lists
• Look for equivalent output events
• Look for variable groups that must calculate to a certain value or range