Test Case Design Techniques in Software Testing: Elements, Types, and Best Practices

“Testing is a skill. While this statement is obvious, it is profound in its implications.” Bret Pettichord, software architect.

The first step in software testing should always be taken with caution. When testing an app or website, how do you decide what to test? Which features do you prioritize?

That’s where having a robust understanding of test case design techniques is vital. They’re responsible for setting the foundational success of your software. In this blog post, we’ll learn all about the top test case design techniques in software engineering.

But first, let’s start with the basics.

Definition of Test Case Design

It involves creating a structured list of steps, scenarios, and conditions to verify a software feature meets the desired performance and reliability. A test case design effectively uncovers defects in the software and ensures it behaves as expected under various conditions.

Elements of Test Case Design Strategies in Software Testing

A test case design comprises the following elements:

Test objective: Every test has a purpose. What is it that you’re trying to validate? The objective helps you define what needs to be tested, why, and what the expected outcome should be.

Test input or precondition: Identify what data or actions are required to execute the test. A precondition specifies any necessary setup before testing begins.

Test coverage criteria: Identify which aspects of your software should be tested for completeness. Different test design techniques result in different coverage levels.

Test condition: This is a specific aspect of the software to be verified. It’s derived from requirements. For instance, users should be able to reset their password on the app.

Resetting the password is a condition.

But ensuring this feature works smoothly for users is a requirement.

Test scenario: It’s a real-world situation that simulates how users interact with the app.

Test data: Good testing depends on good data – both valid and invalid inputs. Include edge cases, empty fields, special characters, and long inputs. Use dynamic test data that updates as needed.

Test environment: Where will the tests run? Check for hardware, software, network settings, and configurations – they should match production as closely as possible.

Test execution and logging: Once a test case is designed, it needs to be executed and results must be logged for tracking issues. Do it manually or through automation.

Types of Test Case Design Techniques

Let’s study the different ways you can design test cases systematically. Catch bugs early, cover more ground, and avoid testing unnecessary things.

1. Black-box testing

It’s a technique that examines how a software works by providing inputs and observing the outputs. For example, if the app should do X when you input Y, your job is to confirm that’s what happens. Here’s what comes under black-box testing:

a. Boundary Value Analysis (BVA)

This technique tests the boundary values of valid and invalid partitions.

For example, if a software allows values from 18 to 59, you only test inside the boundary (18, 59) and just outside (17, 60). BVA is especially useful in numeric input fields, range-based validation, and limit-based conditions.

b. Equivalence Partitioning (EP)

It’s a technique that divides input domains into classes of data – with the help of which test cases can be derived. That means instead of testing every value, you test one from each group and assume the rest behave the same.

For instance, if a form is supposed to accept ages between 18 and 59, you don’t need to test every single age. Just pick a few: maybe one from the valid range (30), one below (17), and one above (60). This allows you to test all conditions without any repetition.

c. Decision table testing

A decision table lays out all possible inputs and their expected results so you can systematically cover them. For instance, in a login system that requires a valid username, correct password, and an optional 2FA, you’d list every combination of these conditions.

This technique helps you catch issues where the software might behave unexpectedly when conditions mix.

d. State transition testing

If your software changes based on user actions, state transition testing ensures it handles different states and unexpected user actions. For example, if you enter the correct passcode, it should unlock. If you enter the wrong passcode three times, it should lock temporarily. If you wait a few minutes, it should let you try again.

e. Pairwise testing

Some inputs in an app interact with each other. Suppose you’re testing a flight booking system with three inputs – arrival city, departure city, and class type. Pairwise testing covers each pair of inputs at least once – without testing every single combination.

2. White-box testing

White-box testing analyzes an app’s internal structure and logic. Your goal is to ensure every part of it runs at some point during testing.

a. Statement coverage

This is the simplest white-box testing technique. Here, you execute all the paths, lines, and statements of the source code at least once to spot undetected bugs.

b. Decision coverage

Every time your code makes a decision, for instance, an if-else statement or a switch case, both true and false paths should be tested.

For instance, if you have a discount system where users get a discount if they spend over $100, you need one test case where the user spends $101 (true path) and another where they spend $99 (false path).

c. Single and multiple condition coverage

Single condition coverage is a type of test case design technique that’s primarily focused on covering all the conditions in the software source code. Here, every Boolean expression described in the conditions expression (e.g., OR, AND) is evaluated to both true and false outcomes.

In multiple condition coverage, we test all possible combinations of the conditions to ensure every logical path is evaluated.

For example, in the condition (A or B) and C, multiple condition coverage tests all possible combinations like (True, False, True), (False, True, False), etc., to ensure every logical path is evaluated.

Both test case design techniques are important for a comprehensive testing process.

d. Path testing

This involves designing test cases to test all possible paths in the program at least once. If your code has three different if-else branches, it ensures all three get tested, including combinations where different branches run together.

e. Data flow testing

Variables move throughout the code – they get created, modified, or used. Data flow testing checks whether they’re used correctly and whether any uninitialized or wrongly modified values exist. This technique helps find hard-to-spot bugs, like using a variable before it’s been assigned a value.

3. Experience-based test design techniques

This isn’t your typical technique. It’s a dynamic approach that relies on a tester’s intuition, skills, and past experiences. Its ability lies in uncovering test scenarios that might slip through the cracks of other rigid methodologies.

Let’s take a look at experience-based test case design techniques:

a. Error guessing

If you’ve tested enough apps, you’ll start noticing patterns – places where bugs always seem to pop up. Maybe entering special characters in input fields of the app is causing crashes. Maybe hitting back on a payment screen is breaking the process.

Error guessing involves testing areas that are likely to fail based on past knowledge.

b. Exploratory testing

Here, you interact with the app like a real user. You try different inputs, navigate the app unexpectedly, and push buttons in ways that might break something. Exploratory testing enables you to test things you wouldn’t do formally.

This is one of the test case design techniques that’s perfect for validating new features, complex workflows, and UI-heavy apps.

Test Case Design Techniques: Best Practices for Implementing Them

When writing a test case, you should ensure it’s clear, maintainable, and actually useful. Here’s how to make the most of test case design techniques:

Be as precise as possible. Simplify each step. Your test case shouldn’t have more than 15 steps. The QA engineer should be able to follow all the information and ensure run adequate tests to deliver the expected outcome.

Always think about the end user when writing the test cases. You want them to reflect every part of the user journey. Use the Specifications and Requirements Documents to do so.

If multiple tests can be executed with the same test case, use the Test Case ID to refer to the required test case.

Try to achieve maximum test coverage. While 100% is rarely possible, ensure that critical functionalities, edge cases, and high-risk areas are thoroughly tested. Use different test case design techniques like BVA and EP for superior results.

Write self-cleaning test cases. You want to make sure the tests restore the environment to its original state after execution, preventing leftover data or configuration changes.

Conclusion

Effective software testing requires a strategic approach to test case design, ensuring comprehensive coverage and early bug detection. By leveraging black-box, white-box, and experience-based techniques, testers can validate functionality, performance, and security. Best practices like clear documentation, user-focused scenarios, and maximizing test coverage enhance the process. A well-structured test case design not only improves software reliability but also streamlines the testing workflow. Ultimately, mastering test case design techniques is crucial for delivering high-quality software that meets user expectations.

Source: This blog was originally published at https://testgrid.io/blog/test-case-design-techniques/