Do jest tests wait for previous async tests to resolve? - async-await

Question

I have read that jest tests in the same tests file execute sequentially. I have also read that when writing tests that involve callbacks a done parameter should be used.
But when using promises using the async/await syntax that I am using in my code below, can I count on the tests to but run and resolve in sequential order?
import Client from '../Client';
import { Project } from '../Client/types/client-response';
let client: Client;
beforeAll(async () => {
jest.setTimeout(10000);
client = new Client({ host: 'ws://127.0.0.1', port: 8080 , logger: () => {}});
await client.connect();
})
describe('Create, save and open project', () => {
let project: Project;
let filename: string;
beforeAll(async () => {
// Close project
let project = await client.getActiveProject();
if (project) {
let success = await client.projectClose(project.id, true);
expect(success).toBe(true);
}
})
test('createProject', async () => {
project = await client.createProject();
expect(project.id).toBeTruthy();
});
test('projectSave', async () => {
filename = await client.projectSave(project.id, 'jesttest.otii', true);
expect(filename.endsWith('jesttest.otii')).toBe(true);
});
test('projectClose', async () => {
let success = await client.projectClose(project.id);
expect(success).toBe(true);
});
test('projectOpen', async () => {
project = await client.openProject(filename);
expect(filename.endsWith('jesttest.otii')).toBe(true);
});
})
afterAll(async () => {
await client.disconnect();
})

Answer 1

From the docs:
...by default Jest runs all the tests serially in the order they were encountered in the collection phase, waiting for each to finish and be tidied up before moving on.
So while Jest may run test files in parallel, by default it runs the tests within a file serially.
That behavior can be verified by the following test:
describe('test order', () => {
let count;
beforeAll(() => {
count = 0;
})
test('1', async () => {
await new Promise((resolve) => {
setTimeout(() => {
count++;
expect(count).toBe(1); // SUCCESS
resolve();
}, 1000);
});
});
test('2', async () => {
await new Promise((resolve) => {
setTimeout(() => {
count++;
expect(count).toBe(2); // SUCCESS
resolve();
}, 500);
});
});
test('3', () => {
count++;
expect(count).toBe(3); // SUCCESS
});
});

Answer 2

For sure it depends on test runnner configured. Say for Jasmine2 it seems impossible to run tests concurrently:
Because of the single-threadedness of javascript, it isn't really possible to run your tests in parallel in a single browser window
But looking into docs' config section:
--maxConcurrency=
Prevents Jest from executing more than the specified amount of tests at the same time. Only affects tests that use test.concurrent.
--maxWorkers=|
Alias: -w. Specifies the maximum number of workers the worker-pool will spawn for running tests. This defaults to the number of the cores available on your machine. It may be useful to adjust this in resource limited environments like CIs but the default should be adequate for most use-cases.
For environments with variable CPUs available, you can use percentage based configuration: --maxWorkers=50%
Also looking at description for jest-runner-concurrent:
Jest's default runner uses a new child_process (also known as a worker) for each test file. Although the max number of workers is configurable, running a lot of them is slow and consumes tons of memory and CPU.
So it looks like you can configure amount of test files running in parallel(maxWorkers) as well as concurrent test cases in scope of single worker(maxConcurrency). If you use jest as test runner. And this affects only test.concurrent() tests.
For some reason I was unable to find anything on test.concurrent() at their main docs site.
Anyway you can check against your environment by yourselves:
describe('checking concurrent execution', () => {
let a = 5;
it('deferred change', (done) => {
setTimeout(() => {
a = 11;
expect(a).toEqual(11);
done();
}, 1000);
});
it('fails if running in concurrency', () => {
expect(a).toEqual(11);
});
})
Sure, above I used Jasmine's syntax(describe, it) so you may need to replace that with other calls.