Jest Tutorial For Beginners: Different Ways of Running Test [3/4]

Before moving forward I would suggest that take please check the previous section for the basics of jest test and project configurations.

In this section, we will further deep dive in jest.

Different Ways of Running test:

The command npm test or npm run test will run all test suites available in the project.

Running 1 test case or 1 test suite

Method-I
To run a specific test suite (test-file) run this command npm test -- <file_name>. For that all the below three commands are correct.

npm test -- sum

npm test -- sum.test

npm test -- sum.test.js

To run a specific test (test_case) run this command

npm test -- -t "<test_case_name>"

• Considering our previous example, in that example, the test case name is add so for that we have to write a command like this
  

  npm test -- -t add
  

• this has one disadvantage, against the above command all the .test.js files will be searched for add and all tests will execute.

• Also if any test case has the word add that will execute no matter which .test.js file it is.

• these all because the command -t helps us to set the regular expression and it can math any test case string.

The batter solution for the above scenario is to combine the test suite name and test case name to restrict the command more like

npm test -- sum.test.js -t add

• But still, more than one test case can be run if there is any test case in a test_suite that has the word add.

Method-II - Using .only()

When you mark the single test_case with only() the jest will run only for test_cases that are defined with the method only() and skip all the other test_cases.

you can mark or define more than one test_cases with only().

This will help to restrict the command for jest. now the previously discussed command will work correctly

npm test -- sum.test.js

Example
sum.test.js file

const sum = require("../sum")
test.only("2 + 2 equal 4, add",()=>{
    expect(sum(2,2)).toBe(4);
});

test("add",()=>{
    expect(sum(2,4)).toBe(6);
});

After running the command npm test -- sum.test.js you will get the following result.

 PASS  __test__/sum.test.js
  √ 2 + 2 to equal 4, add (5 ms)
  ○ skipped add

Method-III - Watch Mode

Watch mode has advantages one of them is that it will look for changes in .test.js files and will re-test for changes.

Secondly, after starting testing or looking at changes in .tes.js files it will generate a menu to quickly select an action.

To do so run the following command

npm test -- --watch

After running the above command you will get the menu as shown below:

Watch Usage
 › Press f to run only failed tests.
 › Press o to only run tests related to changed files.
 › Press p to filter by a filename regex pattern.
 › Press t to filter by a test name regex pattern.
 › Press q to quit watch mode.
 › Press Enter to trigger a test run.

Now select the option whatever you want.

Getting the test report in a pretty form:

To get the pretty result of the test use the following command

npm test --coverage

The above command will give the result in the following form:

 PASS  __test__/index.test.js
 PASS  __test__/sum.test.js
----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |                   
 sum.js   |     100 |      100 |     100 |     100 |                   
----------|---------|----------|---------|---------|-------------------

Test Suites: 2 passed, 2 total
Tests:       1 skipped, 2 passed, 3 total
Snapshots:   0 total
Time:        2.27 s
Ran all test suites.

Note: as you may notice the in result that all the test suites (test_files) and the test cases in it are execute my jest.

Conclusion:

Note: if you are the bagginer then i will suggest to not follow whatever suggested in the conlusion.

So try to use the short command for all the techniques you have seen so far. This will not only save your some time, but also improve the overall develper experience.

Set the commands in your package.json file.

{
...
  "scripts": {
    "test": "jest",
    "testw": "jest --watch",
    "testc": "jest --coverage",
...
  },
  "devDependencies": {
    "jest": "^18.1.0",
    ...
  },

}

And if you are using the vs code than install the jest runner extension to save more time.

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