12.3 Program Testing and Maintenance: Choosing Appropriate Test Data

Effective program testing relies heavily on selecting test data that accurately reflects the intended use of the software and helps to uncover potential errors. This section explores the principles of choosing appropriate test data for a comprehensive test plan.

Principles of Test Data Selection

• Boundary Value Analysis: Testing at the edges of valid input ranges. This is a highly effective technique for finding errors related to incorrect handling of minimum and maximum values.
• Equivalence Partitioning: Dividing input data into classes (partitions) that are expected to behave similarly. Testing one value from each partition can significantly reduce the number of test cases.
• Valid Data: Test data that is within the expected range and format. This verifies the correct handling of normal operations.
• Invalid Data: Test data that is outside the expected range or in an incorrect format. This checks for error handling and robustness.
• Stress Testing: Using extreme or very large input values to test the program's stability and resource usage.
• Typical Use Cases: Data that represents common or frequently used scenarios.
• Edge Cases: Unusual or rarely used input values that might expose hidden errors.

Types of Test Data

Test data can be categorized based on its nature and purpose:

• Numerical Data: Integers, floating-point numbers, decimals.
• String Data: Textual values, including empty strings, special characters, and long strings.
• Boolean Data: True/False values.
• Date and Time Data: Dates, times, and time zones.
• File Data: Test files with varying sizes and formats.
• Network Data: Simulated network requests and responses.

Example Test Data Table

The following table illustrates examples of test data for a hypothetical program that calculates the area of a rectangle.

Test Case ID	Length	Width	Expected Area	Test Type
TC001	10	5	50	Valid Data
TC002	0	5	0	Boundary Value
TC003	10	0	0	Boundary Value
TC004	-10	5	Error	Invalid Data
TC005	10	-5	Error	Invalid Data
TC006	10.5	5	52.5	Valid Data (Decimal)
TC007	10	5.2	52	Valid Data (Decimal)
TC008	1000000	1000000	$1000000000000$	Stress Test
TC009		5	Error	Invalid Data (Empty String)

Note: The 'Expected Area' column shows the anticipated output for each test case. The 'Test Type' column indicates the testing technique being applied.

Considerations for Test Data

When choosing test data, consider the following:

• Coverage: Ensure the test data covers all possible scenarios and code paths.
• Realism: Use data that reflects real-world inputs as closely as possible.
• Maintainability: Keep test data organized and easy to update.
• Automation: Design test data that can be easily used in automated testing.