Understanding Equivalence Class Partitioning in Software Testing

Dhruvi Sachapara

Apr 22, 2024

12 min read

Understanding Equivalence Class Partitioning in Software Testing

Contents

Consult the author or an expert on this topic.

Schedule a meeting

Imagine you are testing a login system for a banking app. Instead of manually checking every possible user input, isn't it smarter to test only a few carefully selected cases that cover all possible scenarios? That is exactly what Equivalence Class Partitioning (ECP) in software testing helps achieve!

ECP is one of the most efficient black-box testing techniques, and as such, it reduces the number of test cases remarkably without missing any coverage of the test. By using this technique, instead of testing all input values separately, they are divided into equivalence classes, meaning that one test case will represent an entire group of inputs. This saves some time, effort, and resources while conserving the quality and accuracy of testing.

You will understand what equivalence class partitioning is and how it can help you optimize the testing process of your software by the end of this article. Let's begin! 🚀

What is an Equivalence class?

Equivalence Class Partitioning (ECP) is a black box testing technique that increases the efficiency of software testing by partitioning the input data into distinct classes or "equivalence classes." The system, in each class, is supposed to behave the same way; hence, it becomes possible to select representative inputs from each class rather than testing every possible input. This streamlines the process of testing so that there would be comprehensive coverage with fewer test cases.

Examples to illustrate the concept of ECP

For example, let's consider a scenario where we are testing an age validation feature in a software application. Through equivalence partitioning, we can divide the input values into equivalence partitioning:

Age Validation:
- Valid Class: Ages between 18 and 65 (assuming adult eligibility).
- Invalid Class: Ages less than 18 or greater than 65.‍
‍Username Field:
- Valid Class: Alphanumeric characters (a-z, A-Z, 0-9) and underscores (_).
- Invalid Class: Special characters, empty username, username exceeding a certain length, and empty space before, in-between, and after the username.

Step-by-Step Process of Equivalence Partitioning

This method brings time savings along with efficiency gains while ensuring complete software testing. You can effectively apply the equivalence class partitioning method by taking the help of this step-by-step methodology.

Analyze Requirements and Identify Input Fields

Review the software requirements with completeness before you start developing the equivalence classes.
✔ All input fields in the application
✔ Data types (numeric, string, boolean, etc.)
✔ Expected behavior for different inputs

📌 Example: If the online form needs users to enter their age (from 18 to 60), then the input field should be an integer data type and only things that are within this range should be accepted by the software system.

Identify Equivalence Classes (Valid & Invalid Inputs)

They split them up by the inputs determining if they were valid given that they should have behaved that way.

Inputs the system should accept → Valid Equivalence Class
Inputs the system to reject → Invalid Equivalence Class

📌 Example (Age Field: 18 to 60)

✅ Valid Class 1: Ages between 18-60

❌ Invalid Class 1: Ages below 18

❌ Invalid Class 2: Ages above 60

❌ Invalid Class 3: Non-numeric inputs ("abc", "$$@!")

Why this works? Now only 1 representative value per class (17, 30, 61, ‘abc’) is to be tested instead of all age values.

Define Boundary Values

BVA is done in parallel with ECP, testing out the values at the edge of each equivalence class.

📌 Example (Age Field: 18 to 60)

Lower Boundary Cases: 17 (invalid), 18 (valid)
Upper Boundary Cases: 60 (valid), 61 (invalid)

Testing at these boundaries allows testers to find defects, by being at the boundary of the valid and invalid range.

Select Representative Test Cases

Solving for equivalence classes, select one test case from each class now.

Age Field Selection Test Case

Valid Class: 30 (middle value from the valid range)
Invalid Classes: 17, 61, "ABC" (one from each invalid class)

To minimize the number of test cases while guaranteeing greater effectiveness, we have this.

Execute Tests and Validate Results

Select the test cases to run, and then verify the system’s response.

✔ The correct values should be accepted

✔ Error handling should be triggered with rejected values

Example Expected Outputs:

Input: 30 → ✅ Accepted
Input: 17 → ❌ Error: Age must be 18 or older
Input: "ABC" → ❌ Error: Invalid Input

Benefits of Equivalence Class Partitioning Technique

We have discussed the equivalence partitioning process in the previous section, detailing how it helps organize and streamline testing efforts. Now, let's delve into the various benefits of ECP in software testing to understand why this technique is widely adopted by testers globally.

Now that we have a brief idea of what equivalent class partitioning is and its significance in the world of quality software testing, let's look at the various benefits of ECP to get an idea of why so many testers around the world are using the ECP technique.

Equivalence Class Partitioning works well alongside integration testing methods. Learn more in our System Integration Testing.

Benefits of equivalence class partitioning technique

‍

Reduced Testing Effort
ECP helps us focus on your critical areas, reducing the overall number of test cases.‍
Improved Test Coverage
ECP ensures a wide range of valid and invalid inputs are covered during testing.‍
Targeted Testing
ECP helps identify critical areas, like BVA, for targeted testing.‍
Systematic Approach
ECP promotes a structured and organized way of designing test cases.

Practical Examples of ECP In Software Testing

We have completed the theoretical part of the blog, now we will explore the practical part of the blog, starting with practical examples where we use ECP. We’ll look into various real-life scenarios, ranging from online shopping to discount codes as well.

our expertise in software testing allows us to deliver tailored solutions that meet our clients' unique needs, ensuring thorough and efficient testing processes.

Online Shopping

ECP shines when testing functionalities like adding items to a shopping cart and managing quantities.

The Classes:

Field	Valid Class	Invalid Class
Quantity	Positive integers (1-10)	Negative quantity
Quantity	Zero quantity	Non-numeric characters (abc)
Quantity	Quantity exceeding stock limit

Test Cases:

Test Case ID	Description	Expected Result
TC_01	Add a valid quantity (e.g., 2) of a product to the cart	Product added to cart with correct quantity reflected
TC_02	Try adding a negative quantity of a product	Error message indicating invalid quantity
TC_03	Add zero quantity of a product	Product not added to cart (or message indicating zero quantity)
TC_04	Try adding a large quantity exceeding available stock	Error message indicating insufficient stock or quantity adjusted to available limit
TC_05	Enter non-numeric characters (e.g., "ten") in the quantity field	Error message indicating invalid quantity format

Discount Code

ECP helps ensure discount codes are applied correctly based on their format and eligibility.

The Classes:

Field	Valid Class	Invalid Class
Discount Code	Alphanumeric characters (uppercase and lowercase)	Special characters (@, $, #, etc.)
Discount Code	Valid code format (e.g., "SUMMER10")	Incorrect code format
Discount Code	Case-sensitive code (if applicable)	Code entered with incorrect case (e.g., "summer10" for a case-sensitive code)
Discount Code	Code within its validity period	Expired code

Test Cases:

Field	Valid Class	Invalid Class
Discount Code	Alphanumeric characters (uppercase and lowercase)	Special characters (@, $, #, etc.)
Discount Code	Valid code format (e.g., "SUMMER10")	Incorrect code format
Discount Code	Case-sensitive code (if applicable)	Code entered with incorrect case (e.g., "summer10" for a case-sensitive code)
Discount Code	Code within its validity period	Expired code

Date input

Date formats are used in almost every domain, whether it's an educational site or a shopping site. ECP makes the testing process of these date formats much simpler.

The Classes:

Field	Valid Class	Invalid Class
Discount Code	Alphanumeric characters (uppercase and lowercase)	Special characters (@, $, #, etc.)
Discount Code	Valid code format (e.g., "SUMMER10")	Incorrect code format
Discount Code	Case-sensitive code (if applicable)	Code entered with incorrect case (e.g., "summer10" for a case-sensitive code)
Discount Code	Code within its validity period	Expired code

Test Cases:

Field	Valid Class	Invalid Class
Discount Code	Alphanumeric characters (uppercase and lowercase)	Special characters (@, $, #, etc.)
Discount Code	Valid code format (e.g., "SUMMER10")	Incorrect code format
Discount Code	Case-sensitive code (if applicable)	Code entered with incorrect case (e.g., "summer10" for a case-sensitive code)
Discount Code	Code within its validity period	Expired code

We excel in applying techniques like ECP to ensure comprehensive and efficient testing. Our expertise spans various domains and applications, allowing us to tailor our testing strategies to meet the unique needs of our clients. By leveraging ECP, we help our clients achieve high-quality software that performs reliably in real-world scenarios.

Equivalence Class Partitioning (ECP) vs Boundary Value Analysis (BVA)

Aspect	Equivalence Class Partitioning (ECP)	Boundary Value Analysis (BVA)
Purpose	Eliminates test cases by grouping inputs into equivalence classes	Test boundary values where defects are likely
Approach	Choose one representative value from each class	Focuses on minimum, maximum, and edge values
Use Case	Validates general input conditions	Detects errors at boundaries between input partitions
Example	Age Range 18-60: ✅ Valid: 18-60 ❌ Invalid: <18, >60, "abc"	Test boundaries: 17, 18, 60, 61
Best For	Ensuring broad input coverage with fewer tests	Capturing edge-case defects
Efficiency	High—fewer tests, broad coverage	Moderate—more tests but critical for boundary errors
When to Use	For general functionality testing	When boundaries are critical (e.g., age limits)

Why Combine ECP and BVA?

Efficiency: Use ECP for the reduction of redundant test cases to increase efficiency.
Effectiveness: Use BVA to catch errors in the boundary.‍
Comprehensive Testing: Ensures input scenarios are caught squarely under the blanket of testing.

Avoid common mistakes while considering ECP

By lowering redundancy and boosting coverage, Equivalence Partitioning is an effective testing approach that facilitates the testing process. Like any approach, though, if it isn't used effectively, mistakes might happen. For testing to be effective, it is essential to comprehend these typical errors. Here’s an overview:

Lack of prioritization
‍Not all classes are equally critical. Failing to prioritize them based on risk and importance can lead to inefficient testing and delayed bug detection.
Example of a banking application where users can transfer funds. Classes could include different types of account balances (e.g., positive balance, zero balance, negative balance).
Blindly relying on ECP alone
‍While ECP is an effective technique, it should not be used in isolation. Combining it with other testing techniques, such as boundary value analysis and decision table testing, enhances test coverage and defect detection.
Inadequate handling of complex conditions
‍When dealing with complex systems or input conditions, testers may struggle to properly partition the classes. It’s essential to break down complex scenarios into manageable partitions to ensure solid and complete testing that can handle complex systems. ‍
Overlapping classes
‍When defining partitioning classes, ensure they are distinct and non-overlapping. Overlapping classes can result in redundant tests, undermining the efficiency of ECP.
Neglecting boundary values
‍One of the most common mistakes is overlooking boundary values while partitioning classes. Boundaries often harbor bugs, so failing to include them can lead to inadequate or incomplete test coverage.

Best practices for equivalence class partitioning testing

It’s time for the final section of the blog, “Best Practices” for Using the ECP. We’ll dive deep into the best tips for ECP, how to perform the practice, and what will be the outcome of these tips or their impact on the testing process. After that, we will look at what other techniques we can fuse with ECP.

Understand the System Under Test (SUT)

Before applying ECP, thoroughly understand the system's requirements, functionalities, and user expectations. This understanding forms the basis for identifying relevant input conditions and equivalence Partitioning methods.