Calculating test design coverage involves determining the extent to which your test cases cover the requirements, features, and risks of the system under test. There isn't a single formula; instead, it's a process of defining what you want to cover and then measuring how well your tests achieve that coverage. Here's a breakdown of the process:
1. Define Coverage Goals
Before you can calculate coverage, you need to establish clear goals. What aspects of the system are most critical to test? Common coverage goals include:
- Requirement Coverage: Ensuring that each requirement is addressed by at least one test case.
- Feature Coverage: Verifying that all features of the system function as expected.
- Risk Coverage: Targeting tests at areas of the system with the highest potential for failure or impact.
- Code Coverage: (While technically different, it is related) Covering different code paths, branches, and statements in the code.
2. Identify Coverage Items
Once you know what kind of coverage you want, you need to identify the specific items that need to be covered. This could include:
- Requirements: Individual requirements from your requirements documentation.
- Features: A list of all the features the system offers.
- Risks: A catalogue of potential risks identified during risk analysis.
- Code Elements: (For code coverage) Lines of code, branches, conditions, etc.
3. Map Test Cases to Coverage Items
The next step is to link your test cases to the specific items you've identified. For example, you would link a test case to the requirement it verifies or the feature it tests. This mapping is crucial for calculating coverage. A traceability matrix can be very helpful here.
4. Calculate Coverage Percentage
The basic formula for calculating coverage is:
*Coverage (%) = (Number of Coverage Items Covered by Tests / Total Number of Coverage Items) 100**
For example:
- If you have 100 requirements and your test cases cover 85 of them, your requirement coverage is (85/100) * 100 = 85%.
- If you have 50 features, and your test cases directly exercise 40 of them, your feature coverage is (40/50) * 100 = 80%.
5. Tools and Techniques
Several tools and techniques can assist with calculating test design coverage:
- Test Management Tools: Tools like TestRail, Zephyr, or Xray allow you to link test cases to requirements and track coverage.
- Requirements Management Tools: These tools help manage requirements and can often be integrated with test management tools.
- Code Coverage Tools: Tools like JaCoCo (Java), Istanbul (JavaScript), or gcov (C/C++) measure code coverage by tracking which lines of code are executed by your tests. While this isn't test design coverage, it informs whether or not test cases actually exercise different execution paths.
- Traceability Matrix: A table that maps requirements to test cases. This helps visualize coverage and identify gaps.
6. Interpreting and Improving Coverage
A high coverage percentage doesn't guarantee a bug-free system. It simply indicates that your tests address a significant portion of the defined coverage items. Analyze coverage gaps to identify areas needing more testing and refine your test design to improve overall coverage and quality.
For example, if a low coverage value is reported for risk items, consider writing additional tests for areas considered high risk.
Example Scenario
Imagine you're testing an e-commerce website. You have the following:
- Requirements: 50 user stories outlining the functionality.
- Test Cases: 100 test cases designed to validate the user stories.
After mapping test cases to requirements, you find that 45 user stories are covered by at least one test case.
- Coverage: (45 / 50) * 100 = 90% requirement coverage.
This indicates that 90% of the defined requirements have associated test cases. You would then investigate the 5 uncovered user stories to determine why they aren't covered and create new test cases to address them.
