# Software Testing Techniques with Test Case Design Examples

15/10/2023

Software Testing Techniques are essential for crafting more effective test cases. Given that exhaustive testing is often impractical, Manual Testing Techniques play a crucial role in minimizing the number of test cases required while maximizing test coverage. They aid in identifying test conditions that might be challenging to discern otherwise.

Boundary Value Analysis (BVA)

Boundary Value Analysis (BVA) is a software testing technique that focuses on testing at the boundaries of input domains. It is based on the principle that errors often occur at the extremes or boundaries of input ranges rather than in the middle of those ranges.

Boundary Value Analysis works:

1. Minimum Boundary: Test with the smallest valid input value. This is typically one less than the minimum valid input.
2. Just Above Minimum Boundary: Test with the next value just above the minimum boundary.
3. Middle Value: Test with a value in the middle of the valid range.
4. Just Below Maximum Boundary: Test with the value just below the maximum boundary.
5. Maximum Boundary: Test with the largest valid input value. This is typically one more than the maximum valid input.

The idea behind BVA is to design test cases that verify if the software handles boundaries correctly. If the software works correctly at the boundaries, it is likely to work well within those boundaries as well.

For example, if a system accepts input values between 1 and 10, the BVA test cases would:

• Test with 0 (just below the minimum boundary).
• Test with 1 (the minimum boundary).
• Test with 5 (a middle value).
• Test with 10 (the maximum boundary).
• Test with 11 (just above the maximum boundary).

This technique is particularly effective in uncovering off-by-one errors, array index issues, and other boundary-related problems. It is commonly used in both manual and automated testing.

Equivalence Class Partitioning

Equivalence Class Partitioning (ECP) is a software testing technique that divides the input data of a software application into partitions of equivalent data. The goal is to reduce the number of test cases needed to cover all possible scenarios while maintaining adequate test coverage.

Equivalence Class Partitioning works:

1. Identify Input Classes: Group the possible inputs into different classes or partitions based on their characteristics.
2. Select Representative Values: Choose a representative value from each partition to be used as a test case.
3. Test Each Partition: Execute the test cases using the selected representative values.

The underlying principle of ECP is that if one test case in an equivalence class passes, it is likely that all other test cases in the same class will also pass. Similarly, if one test case fails, it is likely that all other test cases in the same class will fail.

For example, if a system accepts ages between 18 and 60, the equivalence classes would be:

• Class 1: Ages less than 18 (Invalid)
• Class 2: Ages between 18 and 60 (Valid)
• Class 3: Ages greater than 60 (Invalid)

Test cases would then be selected from each class, such as:

• Test with age = 17 (Class 1, Invalid)
• Test with age = 30 (Class 2, Valid)
• Test with age = 65 (Class 3, Invalid)

ECP is a powerful technique for reducing the number of test cases needed while still providing good coverage. It is particularly useful for situations where exhaustive testing is impractical due to time and resource constraints. ECP is commonly used in both manual and automated testing.

Decision Table Based Testing

Decision Table Based Testing is a software testing technique that helps identify different combinations of input conditions and their corresponding outcomes. It is particularly useful when testing systems with a large number of possible inputs and conditions.

Decision Table Based Testing works:

1. Identify Conditions: List down all the input conditions that can affect the behavior of the system.
2. Identify Actions or Outcomes: Determine the actions or outcomes that are dependent on the combinations of input conditions.
3. Create a Table: Create a table with columns representing different combinations of conditions and rows representing the possible outcomes.
4. Fill in the Table: Populate the table with possible combinations of conditions and their corresponding outcomes. Each cell in the table represents a specific test case.
5. Generate Test Cases: Based on the combinations in the decision table, generate test cases to be executed.
6. Execute Tests: Execute the generated test cases and verify the actual outcomes against the expected outcomes.

The key advantage of Decision Table Based Testing is that it helps ensure comprehensive test coverage by systematically considering various combinations of input conditions.

For example, consider a simple decision table for a login system:

Conditions:

• Username entered (Yes/No)
• Password entered (Yes/No)

Actions:

• Allow login (Yes/No)

Decision Table:

 Condition 1 (Username) Condition 2 (Password) Allow Login? Yes Yes Yes Yes No No No Yes No No No No

In this example, there are four possible combinations of conditions. Each combination results in a different action. This decision table can be used to generate specific test cases to ensure comprehensive testing of the login system.

Decision Table Based Testing is a systematic and structured approach that helps ensure that a wide range of input combinations are tested, making it an effective technique for complex systems.

State Transition

State Transition Testing is a software testing technique that focuses on testing the behavior of a system as it undergoes transitions from one state to another. This technique is particularly useful for systems where the behavior is determined by its current state.

State Transition Testing works:

1. Identify States: List down all the possible states that the system can be in. These states represent different conditions or modes of operation.
2. Identify Events: Determine the events or actions that can trigger a transition from one state to another. These events could be user actions, system events, or external inputs.
3. Create a State Transition Diagram: Create a visual representation of the system’s states and the transitions between them. This diagram helps in understanding the flow of states and events.
4. Define Transition Rules: Specify the conditions or criteria that must be met for a transition to occur. These rules are often associated with specific state-event combinations.
5. Generate Test Cases: Based on the state transition diagram and transition rules, generate test cases that cover different state-event combinations.
6. Execute Tests: Execute the generated test cases, ensuring that the system behaves correctly as it transitions between states.

The goal of State Transition Testing is to verify that the system transitions between states as expected and that the correct actions are taken in response to events.

For example, consider a traffic light system with three states: Red, Yellow, and Green. The events could be “Press Button” and “Timeout”. The State Transition Diagram would depict the transitions between these states based on these events.

State Transition Diagram:

[Press Button]                          [Timeout]

Red ————–> Green ————–> Yellow ————–> Red

Based on this diagram, test cases can be generated to cover various state-event combinations, such as:

• Transition from Red to Green on “Press Button”
• Transition from Green to Yellow on “Timeout”
• Transition from Yellow to Red on “Press Button”, and so on.

State Transition Testing is particularly useful for systems with well-defined states and state-dependent behavior, such as control systems, user interfaces, and embedded systems. It helps ensure that the system functions correctly as it moves through different operational states.

Error Guessing

Error Guessing is an informal software testing technique that relies on the tester’s intuition, experience, and creativity to identify and uncover defects in the software. This technique does not follow predefined test cases or formal test design methods, but rather relies on the tester’s ability to think like a user and anticipate potential problem areas.

Error Guessing works:

1. Informal Approach: Error Guessing is an informal and unstructured approach to testing. Testers use their knowledge of the system, domain, and past experiences to identify potential areas of weakness.
2. Intuition and Creativity: Testers rely on their intuition and creativity to come up with scenarios and inputs that may reveal hidden defects. This can include using unconventional inputs, boundary values, or exploring unusual user interactions.
3. No Formal Test Cases: Unlike formal testing techniques, Error Guessing does not rely on predefined test cases. Testers generate ad-hoc test scenarios based on their hunches and assumptions.
4. Domain and User Knowledge: Testers draw on their understanding of the domain and user behavior to anticipate how users might interact with the software and where potential problems might occur.
5. Experience-Based: Testers with extensive experience in testing similar systems are often more effective at using Error Guessing, as they can draw on their past experiences to identify likely areas of concern.
6. Exploratory Testing: Error Guessing often goes hand-in-hand with exploratory testing, where testers actively explore the software to uncover defects without a predefined script.
7. Highly Subjective: The effectiveness of Error Guessing can vary greatly depending on the tester’s knowledge, intuition, and ability to think critically about potential problem areas.
8. Supplementary Technique: Error Guessing is often used in conjunction with other testing techniques and is not meant to replace formal testing methods.

While Error Guessing is not as structured as other testing techniques, it can be a valuable addition to a tester’s toolkit, especially when used by experienced and intuitive testers who are familiar with the system and its potential weaknesses. It’s particularly useful for identifying defects that may not be easily uncovered through formal test cases.

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