___ # **Test Coverage** ___ --- #### What is test coverage? *test coverage is a **measure** used to describe the degree to which the source code of a program is executed when a particular test suite runs.* *In other words - Test Coverage - is **the number of lines of code in the software being tested**.* --- #### *e.g* *If the total lines of code in a system component is 1000 and the number of lines being actually executed through all existing test cases is 650, then your test coverage is:* > `(650 / 1000) * 100 = 65%` --- #### Why is test coverage useful? - *Test coverage helps improve your chances of catching all the critical/high priority bugs.* - *To find the areas in specified requirement which is not covered by the test scenarios and cases.* - *The check on quality of the application.* --- #### What is nyc? how is it related to test coverage? *"nyc" is a package of "istanbul". And it used to get the **test coverge**.* *To use nyc we need to update the "package.json" by installing a package manager to add it as a dev dependency using* > sudo npm install -D nyc -g --- *When we use nyc we call npm scripts and insert it to scripts block* ``` {   "scripts": {     "test": "mocha",     "coverage": "nyc npm run test"   } } ``` *run using terminal* > nyc npm run test --- *nyc generated how much line percentage has been covered for example:*  --- *prefer the icov-report: shortcut to running this command:* > nyc report –reporter =icov --reporter=text ---  --- ### Does 100% coverage mean you have tested everything correctly? --- *Well NO! Because even if all your classes have 100% coverage, that still doesn’t mean they will correctly interact with each other.* --- for example: ``` public class Calculator { public int sum(int a, int b) { return a+b; } } ``` *here we can see that the code coverage is 100%. are you sure every thing will work as expected for that class?* *NO* :stuck_out_tongue: --- *This is because code coverage doesn’t tell you anything about the quality of your tests. It only counts what lines of code are executed during tests and what aren’t.* --- A good Calculator test (with 100% line coverage) would be: ``` @Test public void sumOfOneAndThreeShouldBeFour() throws Exception { int result = new Calculator().sum(1,3); assertEquals(4, result) } ``` --- ``` public class Calculator { public int sum(int a, int b) { return 4; } } ``` All above tests would still pass, code coverage would be 100% but your code doesn’t functionally do what it should. We would need to add multiple tests (covering the same line of code) to guarantee that. --- Code coverage != quality of tests So coverage doesn’t ensure your tests: - do an actual assert - are complete (cover all functionality) --- Thank You for listening :ear: