Test Coverage and Code coverage are the most popular methodologies for measuring the effectiveness of the code. Though these terms are sometimes used interchangeably since their underlying principles are the same.
But they are not as similar as you may think. Many times, I have noticed the testing team and development team being confused over the use of these two terminologies.
Code Coverage vs Test Coverage: How Do They Differ?
Code coverage : indicates the percentage of code that is covered by the test cases through both manual testing and automation testing with Selenium or any other test automation framework. For example, if your source code has a simple if…else loop, the code coverage would be 100% if your test code would cover both the scenarios i.e. if & else.
Test coverage : includes testing the features implemented as a part of the Functional requirements specification, software requirements specification, and other required documents. For example, if you are to perform cross browser testing of your web application to ensure whether your application is rendering well from different browsers or not? Your test coverage would be around the number of browsers + OS combinations over which you have validated browser compatibility of your web application.
The bases on which the impact of code coverage and test coverage are measured are totally different. Code coverage is measured by the percentage of code that is covered during testing, whereas test coverage is measured by the features that are covered via tests.
The million-dollar question is “Which one of these is best suited for your project”?. There is no definite answer to this question as the solution depends on the type & complexity of the project. In most cases, test coverage and code coverage are used since they are equally important in software projects.
Advantages of Test Coverage
- A good approach to test the software features and compare the results across different specification documents (requirements, feature, product, UI/UX, etc.)
- As the tests performed as a part of the coverage are black-box in nature, executing those tests might not require much expertise.
Shortcomings Of Depending On Test Coverage
- There is no scope of automation as the tests are predominantly black-box tests. Manual comparison of the test results has to be done with the expected output since these tests are performed at a ‘feature level’ and not ‘code level’.
- No concrete way of measuring test coverage. Hence, the coverage results largely depend on the domain competence of the tester who is performing the tests and may vary from one tester to another.
Advantages of Code Coverage
- Provides the effectiveness of your test code and how you can improve the coverage
- Irrespective of the type of tool being used (open-source, premium), setting up a code coverage tool should not take much time.
- Helps in improving the code quality by capturing bugs in the code.
Shortcomings of Code Coverage
- Majority of code coverage tools are limited to unit testing.
- The methodology used by tools could be different hence; you may not be able to compare code coverage results of one tool to another.
- Searching for the best-suited tool could be a big task as you need to compare & try features from those tools before selecting the best one that suits your project requirements.
- There are very few tools that provide support for different programming languages e.g. Java, Python, C, etc. Hence, you may need to have more than one tool in case your team is using multiple programming languages (for test code development).
How Much Coverage Is Enough?
More the number of tests; better would be the quality of the product. There should be frequent communication between the design, development, and test teams so that every stakeholder has detailed information about the activities involved in the project.
The test team should spend a good amount of time in understanding the overall requirements and prioritize the test activities. In order to keep track of the progress, they should have a checklist that should be updated on a periodic basis (at least after every release). It is important that the test team also has frequent communication with the Quality Assurance (QA) team since they have details about the target (test/code) coverage that has to be achieved for the product/project to be released to the client/customer.
To summarize, there is no specific thumb rule which mentions about the minimum percentage of code coverage or test coverage that needs to be achieved while testing the product.