5. Test Case Design Techniques

Test Scenarios vs Test Cases

Definition: A high-level idea of what to test vs. A step-by-step set of instructions to test a feature.

Detail: Broad; covers multiple test conditions vs. Detailed; focuses on one specific path.

Usage: Useful in brainstorming vs. Used for execution, tracking, and reporting.

Test scenarios are broad concepts or ideas about what needs to be tested within a system. For example, 'Verify login functionality' can be a test scenario. In contrast, a test case provides specific instructions on how to execute the test, such as the exact steps to input valid or invalid credentials. Test cases are detailed and focus on particular paths through the software. They are crucial for actual testing and tracking progress.

Think of a test scenario like a 'recipe idea' for a dish, while test cases are the detailed step-by-step instructions for actually cooking that dish. The scenario gives you an idea of what you want to create, while the test case tells you exactly how to do it.

Boundary Value Analysis (BVA)

Definition: A technique that tests the edges or boundaries of input ranges, where most defects tend to occur.

Where to Use: When input is taken in a range (e.g., age, price, quantity).

Example: Field: Age (Allowed: 18–60)

Rule: Always test min, max, just below, just above, and the values in between.

Boundary Value Analysis focuses on testing the limits of input values. For instance, if a system accepts ages between 18 and 60, we want to test not only 18 and 60 but also values just below (17) and just above (61) these limits. The rules imply that since defects often occur at the edges of input ranges, careful testing in these areas is crucial.

Imagine you’re checking the height for a roller coaster ride. The minimum height is 48 inches. You would want to measure 48 inches (just right), 47 inches (too short), and even the maximum limit the coaster allows, like 72 inches, alongside 73 inches (too tall) to ensure safety regulations are met.

Equivalence Partitioning (EP)

Definition: Divides input data into equivalent classes, where one test from each class represents the whole group.

Where to Use: When input values can be grouped logically (valid/invalid classes).

Example: Field: Age (Allowed: 18–60)

Tip: Save time by testing just one value from each class instead of every value.

Equivalence Partitioning helps in reducing the number of test cases. Instead of testing every individual input value, it groups them into classes where all values in a class are expected to behave the same way. For example, if the allowed age is 18-60, testing one value from the valid range (like 25) suffices, while any invalid inputs would only need one test case each (like 10 and 70) to show they are rejected.

Think about attending a movie based on age restrictions. Instead of checking every age, you just need to test a single valid age and a couple of invalid ages (like someone who's 10 and someone who's 70) to see if the system correctly identifies the allowed age range.

Decision Table Testing

Definition: A tabular method to handle complex business rules involving combinations of conditions and actions.

Where to Use: When there are multiple conditions and decision-based outputs (e.g., eligibility, pricing).

Example: Scenario: Loan Approval

Tip: Each row in the table represents a unique combination of inputs and outcomes.

Decision Table Testing is effective when multiple criteria lead to varying outcomes. By organizing these interactions in a table, testers can visually represent different conditions and their respective actions. For instance, if a loan is dependent on both income and credit score, we can quickly see under what circumstances a loan is approved, reviewed, or rejected based on various combinations of these factors.

Consider a simple recipe where you're deciding what to serve based on guest preferences and dietary restrictions. You could create a decision table that outlines the different combinations of preferences (vegan, gluten-free) and decide what dishes to serve based on that. This way, you can simplify menu planning significantly.

State Transition Testing

Definition: Used to test system behavior for different states and transitions based on events or inputs.

Where to Use: When the system has multiple states (e.g., login, logout, lock) and transitions based on actions.

Example: ATM Login Flow

Tip: Helps ensure the system handles valid and invalid transitions correctly.

State Transition Testing involves examining how a system behaves when it switches from one state to another based on inputs. For example, in an ATM system, entering the correct PIN moves the user from 'Card Inserted' to 'Access Menu', while entering the wrong PIN multiple times leads to the 'Card Blocked' state. This testing confirms that the system behaves correctly at each state and transition.

Think about a smart door lock system. The lock can be in several states: locked, unlocked, or jammed. Depending on whether the right key is used or if the lock is manually manipulated, the lock moves to different states. Testing this ensures that the mechanism behaves correctly under various conditions, just as you’d check to make sure a door lock opens and closes properly based on the right keys and actions.

Summary of Techniques

This summary table encapsulates the core techniques we've discussed, highlighting where each is best applied. For example, Boundary Value Analysis works well for numeric ranges, such as age limits, whereas Equivalence Partitioning is ideal for scenarios involving valid and invalid inputs like form fields. Decision Tables help manage complex rules, and State Transition Testing is essential for systems that experience various states.

Consider a grocery store. Different sections (like dairy, produce, bakery) represent various test techniques. Just as you wouldn’t use the same method to check for frost in the freezer section as you would to evaluate the bread freshness, each testing technique serves a unique purpose tailored to specific scenarios.

Tips for Test Designers

• Always combine EP and BVA when working with input fields.
• Use Decision Tables to catch hidden combinations.
• Use State Transition Diagrams for workflow-heavy applications.
• Keep test cases traceable to requirements.

These practical tips provide guidance for test designers to improve the effectiveness of their testing process. For example, combining Equivalence Partitioning and Boundary Value Analysis harnesses their strengths, making testing more efficient. Additionally, using Decision Tables can help uncover complex interactions that might not be immediately apparent. Keeping test cases aligned with requirements ensures that tests remain relevant and targeted.

Consider a top chef using a checklist to ensure that ingredients are both high quality and in the ideal state before cooking. Each tip acts like a tool in their toolkit, making the testing process smoother and more thorough, ensuring that nothing essential is overlooked, much like ensuring each dish served is perfect.

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