Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

jest: How to teardown after (just) an individual test

jest provides afterEach, beforeEach, afterAll and beforeAll to complete setup and teardown logic. What I would like to do, is to clear up after one particular test. Consider the following:

describe("a family of tests it makes sense to group together", () => {
    ...
    test("something I want to test", () => {
        // some setup needed for just this test
        global.foo = "bar"
        
        // the test
        expect(myTest()).toBe(true)

        // clear up
        delete global.foo
    }
    ...
}

The problem with the above...

If the test above fails for some reason, then delete global.foo is never run. This means that potentially all of the tests following it will fail. Rather than seeing 1 test fail, I see a whole load of tests fail, which could be confusing.

Potential (non-ideal) solutions

One solution is just to add delete global.foo into my afterEach. It doesn't really need to be run after every test, but it doesn't do any harm either. Another solution would be to put the particular test by itself so that afterEach would only apply to it. But this doesn't seem ideal either - if that test belongs with other tests, it aught to be possible for it to remain with them.

My question:

Is there a way to run teardown logic for just a specific test (without running it inside the actual test). In my particular use-case the first outlined solution is fine, but I can imagine there might be situations where finer grained control is needed. If my teardown method took a long time for example I wouldn't want to repeat it lots, as this would slow down the whole test-suite.

like image 263
tim-mccurrach Avatar asked Jul 17 '20 16:07

tim-mccurrach


People also ask

Does teardown run after every test?

Code in a teardown() block is run upon completion of a test file, even if it exits with an error.

How do you test only one test in Jest?

It's in the Jest documentation. Another way is to run tests in watch mode, jest --watch , and then press P to filter the tests by typing the test file name or T to run a single test name.

What does cleanup do in Jest?

cleanup ​ Unmounts React trees that were mounted with render. Please note that this is done automatically if the testing framework you're using supports the afterEach global and it is injected to your testing environment (like mocha, Jest, and Jasmine). If not, you will need to do manual cleanups after each test.

What is the difference between beforeAll and beforeEach?

If you're certain that the tests don't make any changes to those conditions, you can use beforeAll (which will run once). If the tests do make changes to those conditions, then you would need to use beforeEach , which will run before every test, so it can reset the conditions for the next one.


1 Answers

In many cases tests can share a common afterEach clean-up even if it's needed for one of them, as long as it doesn't affect others.

Otherwise, this is what block structure is responsible for. One or several tests can be grouped with nested describe just to have their own afterEach, etc blocks, and the only downside is that it makes the report less pretty:

describe("a family of tests it makes sense to group together", () => {
    ...
    describe("something I want to test", () => {
        beforeEach(() => {
            global.foo = "bar"
        });
   
        test("something I want to test", () => {
            expect(myTest()).toBe(true)
        }

        afterEach(() => {    
            delete global.foo
        });
    });

beforeEach and afterEach can be desugared to try..finally:

test("something I want to test", () => {
    try {
        global.foo = "bar"
        
        expect(myTest()).toBe(true)
    } finally {
        delete global.foo
    }
})

This also allows for asynchronous tests but requires them to be written with async instead of done.

like image 124
Estus Flask Avatar answered Sep 20 '22 12:09

Estus Flask