Test Design Coverage in Software Testing

Test coverage is the degree to which a test or set of tests exercises a particular program or system. The more code that is covered by a test, the more confidence developers have that the code is free of bugs. Measuring test coverage can be difficult because it is often hard to determine what percentage of the code is actually being executed by a test. In general, however, the more code that is covered by a test, the better.

There are many different types of test coverage, but in general, test coverage is a measure of how much of the code or functionality of a system is being tested by a particular set of tests. For example, if a set of tests only covers 50% of the code, then it has 50% coverage. There are many different ways to measure test coverage, and the level of coverage that is considered acceptable varies from organization to organization. In some cases, 100% test coverage may be required, while in others, 80% may be considered adequate.

One way to think of test coverage is as a spectrum, with lower levels of coverage being less effective and higher levels being more effective. However, it is important to remember that no single level of coverage is right for all situations, and the level of coverage that is appropriate will depend on the specific system under test and the risks involved.

Purpose of Test Coverage  

The purpose of test coverage is to ensure that all code paths in a program are executed at least once during testing. This helps to ensure that all bugs and potential problems are found and fixed before the program is released. Test coverage can be measured in a number of ways, but the most common metric is line coverage, which simply measures the percentage of lines of code that are executed during testing.

• Cover all possible code paths: All code paths should be covered in a test in order to ensure that all parts of the code are executed at least once. This will help to find potential bugs that may be present in the code.
• Important functionality should be covered: All important functionality should be covered in a test in order to ensure that it is working correctly. This includes ensuring that all inputs are handled correctly and that all outputs are as expected.
• Potential bugs should be fixed before release: All potential bugs should be covered in a test in order to ensure that they are found and fixed before the code is released.
• All potential edge cases should be covered: All potential edge cases should be covered in a test in order to ensure that the code behaves as expected in all situations.
• All potential error conditions should be considered: All potential error conditions should be covered in a test in order to ensure that the code behaves as expected in all situations.
• Executed all tests at least once: All tests should be executed at least once in order to ensure that they are actually being run and that they are working as expected.
• Covered all possible input values: All possible input values should be covered in a test in order to ensure that the software can handle them correctly.
• Considered all possible combinations of input values: All possible combinations of input values should be covered in a test in order to ensure that the software can handle all potential combinations correctly.

Test Coverage Metrics

There are many different ways to measure test coverage, but some common metrics include:

• Lines of code covered: This metric simply measures the number of lines of code that are covered by tests. This is a good starting point, but it doesn’t give the whole picture, since some lines of code are more important than others.
• Blocks covered: This metric measures the number of blocks of code (e.g., if-statements, for-loops, etc.) that are covered by tests. This is a more granular metric than lines of code, but it still doesn’t give the whole picture.
• Functions/methods covered: This metric measures the number of functions or methods that are covered by tests. This is a more granular metric than blocks, but it still doesn’t give the whole picture.
• Statements covered: This metric measures the number of statements that are covered by tests. This is the most granular metric, but it still doesn’t give the whole picture.
• Conditions covered: This metric measures the number of conditions (e.g., if-statements, boolean expressions, etc.) that are covered by tests. 

Critical Areas and Methods for Effective Testing 

Areas that may need more testing

• Functionality that is critical to the user or the business: This includes testing essential features of the application to ensure they work as expected. For example, in an e-commerce application, the checkout process would be considered critical functionality. 
• Areas that are most likely to have errors: This includes testing areas of the code that are known to be prone to errors, or that have been identified as being at risk for errors. For example, areas of code that are complex or that have been recently changed are more likely to have errors. 
• New or recently changed code: This includes testing any new or changed code to ensure that it works as expected and does not introduce any new errors. 
• Complex code: This includes testing code that is complex or that has been identified as being at risk for errors. Complex code is often more difficult to test and more likely to have errors. 
• Interfaces to other systems: This includes testing interfaces to ensure that they work as expected and that data is exchanged correctly between the systems.

Methods for Effective Testing

• Use test cases that cover the most important functionality first: It is important to prioritize the test cases so that the most important functionality is tested first. This will ensure that any critical errors are found and corrected as soon as possible. 
• Use test cases that are most likely to find errors: Tests that are most likely to find errors should be given priority so that they can be corrected before the product is released. 
• Use a combination of manual and automated testing: A combination of manual and automated testing can be used to effectively test a product. Automated testing can be used to cover a larger test space quickly, while manual testing can be used to cover specific areas in more detail. 
• Use both positive and negative test cases: Positive test cases test for the expected behavior of the product, while negative test cases test for unexpected behavior. Both types of test cases are important in order to ensure that the product behaves as expected. 
• Use a variety of testing techniques: A variety of testing techniques, such as functional testing, regression testing, and stress testing, should be used in order to get a comprehensive view of the product.

Types of Test Coverage

1. Statement Coverage: A test suite is said to achieve statement coverage if every statement in the software has been executed at least once during testing. This type of test design coverage ensures that every statement in the software has been executed at least once. This is the most basic form of test design coverage and is often used as a starting point for more comprehensive testing.
2. Decision Coverage: A test suite is said to achieve decision coverage if every decision (e.g. if-then-else) in the software has been taken both true and false during testing. This type of test design coverage ensures that every decision (i.e. every ‘if’ or ‘case’) in the software has been executed with all possible outcomes. This is a more comprehensive form of testing than statement coverage and can help to uncover errors that may not be obvious from simply executing every statement.
3. Condition Coverage: A test suite is said to achieve condition coverage if every condition in the software has been evaluated as both true and false during testing. This type of test design coverage ensures that all the conditions within a decision have been executed with all possible outcomes. This is a more comprehensive form of testing than decision coverage and can help to uncover errors that may not be obvious from simply executing every decision.
4. Multi-Condition Coverage: A test suite is said to achieve multi-condition coverage if all combinations of conditions in the software have been evaluated during testing. This type of test design coverage extends condition coverage by testing all the conditions within a decision with all possible combinations of values. This is a more comprehensive form of testing than condition coverage and can help to uncover errors that may not be obvious from simply executing every condition.
5. Modified Condition: A test suite is said to achieve modified conditions if all modified conditions and decisions in the software have been evaluated during testing. This type of test design coverage extends decision coverage by testing all the conditions within a decision with all possible outcomes, taking into account the effect of modifying the conditions. This is a more comprehensive form of testing than decision coverage and can help to uncover errors that may not be obvious from simply executing every decision.
6. Data Flow Coverage: A test suite is said to achieve data flow coverage if all executable paths through the software have been executed during testing. This type of test design coverage ensures that all the possible paths through the software have been executed. This is a more comprehensive form of testing than all the other types of coverage and can help to uncover errors that may not be obvious from simply executing the software.

What does Test Coverage do?

• Measures duration of testing: Test coverage is a measure of how much testing has been done on a particular piece of software. 
• Eliminates defects at early stages: Helps to identify the gaps in requirements, test cases, and defects at early stages of software development. 
• Removes redundant test cases: Test coverage is useful in identifying and removing the test cases that are not much important for the project. 
• Significant impact on ROI: Test coverage can have a significant impact on ROI as early detection and fixing of the defects result in fewer defects at the development stage.
• Gauge the completeness: Test coverage can be used to gauge the completeness of a test suite, and to identify areas of the code that need more testing. 
• The criterion for deciding: It can also be used as a criterion for deciding when to stop testing, as a higher level of test coverage may provide more confidence that the software is free of defects. 
• Improve the quality of software: Test coverage is a valuable metric that can help improve the quality of software. 
• Identify uncovered areas: Test coverage helps to uncover the areas of the code that were not covered by a set of test cases.
• Smooth testing cycles: Test coverage helps in Regression testing, test case prioritization, and test suite management, and can be used to prevent defect leakage using Test coverage analysis.

How Test Coverage Can Be Accomplished?

• Use a testing framework: A testing framework is a set of tools and conventions that simplify and automate the process of writing and running tests. By using a testing framework, you can more easily write and maintain tests, and you can also run multiple tests and track their results.
• Use a coverage tool: A coverage tool is a tool that measures how much of your code is covered by tests. Coverage tools can help you identify which parts of your code are not being sufficiently tested, and they can also help you see the impact of changes to your tests.
• Use both: Using both a testing framework and a coverage tool can give you the best of both worlds: the convenience of a testing framework and the insights of a coverage tool.
• Write tests for all code: This is often easier said than done, but it is important to try to write tests for all code, even if it is not possible to achieve 100% coverage.
• Use a coverage metric: A coverage metric can be used to measure the amount of test coverage achieved. This can be a useful way to track progress and ensure that adequate coverage is being achieved.
• Use multiple test coverage criteria: It can be helpful to use multiple test coverage criteria to get a more comprehensive picture of test coverage. This can help identify areas of your code that need more attention.

Test Coverage vs Code Coverage 

Below are the differences between Test coverage and Code coverage:

Parameters	Test coverage	Code coverage
Definition	Test coverage is a measure of how much testing has been done on a particular piece of code.	Code coverage is a measure of how much code is covered by tests.
Measures	It only measures testing.	It measures both testing and code.
Various other levels	It can be measured at various levels, including statement coverage, branch coverage, and path coverage.	It can be measured at various levels, including line coverage, function coverage, and block coverage.
Percentage of tests	It is often expressed as a percentage of the total number of tests that have been run.	It is often expressed as a percentage of the total number of lines of code that have been covered by tests.
Increased	It can be increased by running more tests.	It can be increased by writing more tests.
Decreased	It can be decreased by deleting tests.	It can be decreased by deleting code.
Find Untested Code	It can be used to find untested code.	It can be used to find both untested and untestable code.
Assess the Quality of Testing	It can be used to assess the quality of testing.	It can be used to assess the quality of both testing and code.

The formula for Test Coverage

There are many factors to consider when calculating test coverage, but ultimately it boils down to this formula:

Coverage = (Number of Tests) / (Number of Lines of Code)

If there are 100 tests and 1000 lines of code, then the test coverage will be 10%. There are a few things to keep in mind when using this formula. 

• First, it only applies to lines of code that are actually executed when the tests are run. So, if there are 1000 lines of code but only 500 are executed when the tests are run, then the test coverage would be 50%.
• Second, the number of tests should be relative to the complexity of the code. If there are 1000 lines of code but only 100 tests, then your coverage might not be very good. On the other hand, if there are 100 lines of code but 1000 tests, then the test coverage is probably quite good.
• Third, this formula only gives a coverage percentage. It doesn’t tell how effective the tests are. For example, there might be 100% test coverage but the tests might not be very good (i.e. they might not find all the bugs).
• Fourth, this formula only applies to unit tests. It doesn’t apply to integration tests, functional tests, etc.
• 100% coverage is not always possible or necessary. It really depends on the project. In some cases, 80% coverage might be good enough. In other cases, you might need 100% coverage.

Example of Test Coverage

There are many different ways to calculate test coverage, but one common method is to simply count the number of lines of code that are executed when the test suite is run. This can be done by manually running the tests and counting the number of lines that are executed, or by using a tool that automatically instruments the code and tracks which lines are executed.

To see an example of how test coverage can be calculated, consider the following simple program:

int add(int a, int b) {

return a + b; }

int subtract(int a, int b) {

return a – b; }

int main() {

int x = 5, y = 3;

int sum = add(x, y);

int difference = subtract(x, y);

return 0; }

Solution:

• This program has 12 lines of code. 
• If we ran a test suite that only exercised the add function, then our test coverage would be 8/12, or 67%. 
• However, if we ran a test suite that exercised both the add and subtract functions, then our test coverage would be 12/12, or 100%.

How should a Good Test Coverage Technique be Implemented?

To implement a good test coverage technique, it is important to select the right coverage metric for the project at hand. The coverage metric should be able to identify areas of the code that are not being adequately tested so that these areas can be given more attention. Furthermore, the coverage metric should be easy to understand and use so that it can be effectively used by all members of the team.

• Define your test coverage goals and requirements: Before you can implement a good test coverage technique, you need to first define your goals and requirements. What do you want to achieve with your test coverage? What are your minimum acceptable coverage levels? Answering these questions will help you choose the right tool and properly configure it.
• Choose a test coverage tool that meets your needs: There are a variety of test coverage tools available, so it’s important to choose one that meets your specific needs. Consider factors such as the programming language(s) you’re using, the type of tests you want to run, and your budget.
• Configure your test coverage tool properly: Once you’ve chosen a test coverage tool, you need to configure it properly. This includes setting the proper coverage levels and choosing the right options for your project.
• Run your test coverage tool regularly and fix any issues that are found: It’s important to regularly run your test coverage tool and fix any issues that are found. This will help ensure that your code is properly covered and that you’re meeting your coverage goals.
• Define what test coverage is and what it means for your project: Test coverage is a measure of how much of your code is executed by your tests. It is important to define what test coverage is and what it means for your project so that you can set appropriate goals and track progress.
• Decide which tests are most important for your project and focus on covering those first: Not all tests are created equal. Some tests are more important than others for ensuring the quality of your software. When prioritizing test coverage, focus on the tests that are most important for your project.
• Use a tool to help measure and track test coverage: There are a number of tools available that can help you measure and track test coverage. These tools can be helpful in ensuring that you are achieving your test coverage goals.
• Make sure all new code is covered by tests and that existing code is regularly reviewed to ensure coverage is still adequate: It is important to ensure all new code is covered by tests. Additionally, it is also important to regularly review existing code to ensure that test coverage is still adequate. This will help to ensure that your software is of high quality.

Benefits of Test Coverage

• Reduced bugs: Test coverage can help reduce the number of bugs in your code. By testing your code, you can find and fix bugs before your users do.
• More reliable code: Code that has been tested is more reliable than code that has not been tested. By testing your code, you can find and fix bugs before your users do.
• Easier to find bugs: Test coverage can help you find bugs in your code. By testing your code, you can find and fix bugs before your users do.
• Faster debugging: By testing your code, you can find and fix bugs before your users do. This can save you time when debugging your code.
• Better code quality: Code that has been tested is typical of higher quality than code that has not been tested. By testing your code, you can find and fix bugs before your users do.
• Reduced time to market: By testing your code, you can find and fix bugs before your users do. This can save you time when releasing your code to the public.
• Ensure that all parts of the code are executed at least once: This is important because it helps to find bugs that might otherwise go unnoticed.
• Prevent regressions: This is important because it helps to ensure that new code does not break old code.
• Ensure that new code doesn’t break old code: This is important because it helps to maintain the stability of the codebase.

Limitations of Test Coverage

• Time-consuming and expensive to set up and maintain: In order to get reliable test coverage, a lot of time and effort must be put into setting up the tests and making sure they are effective. This can be costly, both in terms of money and time.
• Difficult to interpret: The results of test coverage can be difficult to understand and interpret. This can make it difficult to know how effective the tests are and what needs to be improved.
• False sense of security: Having high test coverage can give a false sense of security, as it can make it seem like the system is more robust than it actually is. This can lead to complacency and a lack of vigilance, which can ultimately lead to problems.
• Can miss edge cases: No matter how good the test coverage is, there is always the possibility that it will miss some edge cases. This can lead to problems that only occur in rare circumstances, which can be difficult to find and fix.
• Expensive to calculate and maintain: Test coverage can be expensive to calculate and maintain because it requires running tests and then analyzing the results. This can be time-consuming and may require special tools. Additionally, if the test coverage changes frequently, it can be difficult to keep up with the changes.
• Hard to interpret: Test coverage can be hard to interpret because it is a measure of how many tests were run and how many lines of code were covered. It does not necessarily indicate how effective the tests were at finding bugs.
• Hide problems: Test coverage can be used to hide problems because it can make it seem like the code is better tested than it actually is. This can lead to problems if the tests are not effective at finding bugs.
• Make things seem better than they are: Test coverage can be used to make things seem better than they are because it can make it seem like the code is better tested than it actually is. This can lead to problems if the tests are not effective at finding bugs.