Understanding Equivalence Class Partitioning in Software Testing

Dhruvi Sachapara

Apr 22, 2024

12 min read

Understanding Equivalence Class Partitioning in Software Testing

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Imagine that you are testing the login system of a banking application. Would it be more intelligent to zero in on a small number of carefully selected test cases covering all the scenarios rather than verifying every conceivable user input? Equivalence Class Partitioning (ECP) then becomes very useful!

ECP is a black-box testing technique used for efficiency. It ensures complete coverage and helps to reduce the test case numerate. ECP groups input into equivalence classes rather than testing every input point of interest individually. One test case can thus reflect a whole set of related inputs.

The technique keeps test quality and accuracy while saving time, effort, and money.

What is equivalence partitioning?

A black-box testing technique called equivalency partitioning groups data into sets, so reducing the required test cases while ensuring thorough coverage.

For comprehensive input ranges, especially this approach is quite helpful. Testers divided the data into "equivalence classes," groups expected to behave the same way, instead of testing every value. Choosing one test case from every class lets you test a large range of inputs without looking at every single value.

To assist us in understanding Equivalence Partitioning, let us consider an example.

Example: Testing a Login Form

Suppose that we have a login form containing a username field. In order to apply Equivalence Partitioning, we partition the potential input values into equivalence classes on the basis of expected behavior:

Valid Input Class: Any alphanumeric string (e.g., "user123").
Invalid Input Class 1: Empty username (e.g., "").
Invalid Input Class 2: Special characters (e.g., "@#$%").
Invalid Input Class 3: Input with spaces (e.g., "user name").

Now, instead of testing every possible username, we can select one representative value from each equivalence class:

Valid Input: "user123"
Invalid Input 1: ""
Invalid Input 2: "@#$%"
‍Invalid Input 3: "user name"

Step-by-Step Process of Equivalence Partitioning

This technique saves time and increases efficiency while guaranteeing effective software testing. You can effortlessly implement Equivalence Class Partitioning using this easy, step-by-step procedure.

Analyze Requirements and Identify Input Fields

Review the software requirements with completeness before you start developing the equivalence classes.

✔ All input fields within the application.
✔ Data types (numeric, string, boolean, etc.)
✔ Expected behavior for various inputs.

📌 Example: When the online form requires users to input their age (between 18 and 60), then the input field must be of integer data type and only items within this range should be accepted by the 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

With a clear understanding of what ECP is and its importance in software testing, it’s time to explore why so many testers around the world rely on this technique.

Equivalence class partitioning works seamlessly with integration testing methods. Learn more in our system integration testing section.

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 done the theoretical section of the blog, now let's visit the practical section of the blog, beginning with practical scenarios in which we utilize ECP. We will explore some real-life situations, starting from online shopping to discount coupons as well.

Our software testing expertise enables us to provide customized solutions that fulfill our client's individual requirements, ensuring effective and comprehensive 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 reducing redundancy and increasing coverage, Equivalence Partitioning is a powerful testing method that makes the process of testing easier. As with any method, however, if it isn't properly utilized, errors may occur. To make testing effective, it is important to understand these common faults. Here's a rundown:

Lack of prioritization
‍Not all classes are of the same importance. Not prioritizing them according to risk and severity may result in ineffective testing and late bug detection.
Blindly relying on ECP alone
While ECP is a good technique, it has to be used in combination. Using it along with other testing methods like boundary value analysis and decision table testing improves test coverage and defect detection.
Inadequate handling of complex conditions
In case of intricate systems or input conditions, testers might not be able to divide the classes into appropriate partitions. It's crucial to split complicated scenarios into tractable partitions in order to guarantee strong and comprehensive testing capable of managing complicated systems.
Overlapping classes
The most frequent error is not considering boundary values while partitioning classes. Boundary values are where bugs tend to hide; missing them can lead to poor or incomplete test coverage.
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

Now that we know what equivalence class partitioning (ECP) is, let's move on to the best practices of how to use it to enhance your testing process and outcome.

Understand the System Under Test (SUT)

Prior to using ECP, comprehend the requirements, functionalities, and expectations of the system completely. This is critical in order to identify input conditions and formulate effective equivalence classes.