How to test with Jest?

[geoidesic]

Hi,

I'm trying to figure out how to write tests using this library. I looked at fake-indexeddb/auto and while this seems to work partly I end up with an instance of idb that doesn't have a put method. I looked at the mocha tests included in the lib... but I didn't understand them – they seem to have been written without mocking IndexedDB at all?

Here's what I tried:

import actions from "../actions";
import IndexedDB from "fake-indexeddb/auto";
import { openDB } from "idb/with-async-ittr-cjs"; 

class DbService {
  instance = void 0;
  async initialize() {
    this.instance = await openDB("MNR", 2, {
    ...
    })
  }
};
const db = new DbService();
db.initialize();
test("IDB_resetBusy to call put", async () => {
    await db.initialize();
    db.instance.put = jest.fn();
    await actions.IDB_resetBusy("blah");
    expect(db.instance.put).toHaveBeenCalledTimes(1);
  });

I get the error:

TypeError: Cannot read property 'put' of undefined

[jakearchibald]

I deliberately don't test with a mock, as it's more important for me to see how it works with actual indexeddb.

Closing this, as it isn't an issue with the library, but I'm happy to continue answering questions etc.

[geoidesic]

Thank you Jake. What I'm not understanding is that IndexedDB only exists in browser. Unit tests don't have a browser, thus do not have IndexedDB. So how is it possible to test without a mock?

[jakearchibald]

I'm not sure. Fwiw I tend to only write integration tests for things that involve indexeddb, because it's more important for me to test real indexeddb than a mock.

[geoidesic]

I understand that. I just don't understand how you are able to test real IndexedDB as it only exists in browsers and afaik mocha doesn't provide that capability, so IndexedDB should evaluate to undefined... it does when I try it and is the reason for the existence of libraries such as fake-indexeddb/auto.

[jakearchibald]

Mocha runs in the browser

[zquancai]

Thank you Jake. What I'm not understanding is that IndexedDB only exists in browser. Unit tests don't have a browser, thus do not have IndexedDB. So how is it possible to test without a mock?

I think you can use karma to run in the browser.

[taxilian]

While it would be good to do real tests with karma or similar, there are definitely advantages to testing with something like jest or mocha as well using mocks. I have unit tests working with jest, fake-indexeddb, and idb by doing the following:

• Make sure you're using the cjs import if you are using async iterators -- i.e. import * as idb from 'idb/with-async-ittr-cjs'; because with-async-ittrdoesn't work in node, at least not from normal files (probably is a way, I'm too lazy to track it down)
• In your jest.config.js add "fake-indexeddb/auto" to the setupFiles, e.g.:

module.exports = {
  preset: '@vue/cli-plugin-unit-jest/presets/typescript-and-babel',
  transform: {
    '^.+\\.vue$': 'vue-jest'
  },
  setupFiles: [
    "fake-indexeddb/auto"
  ]
}

Beyond that things Just Work so far. Remember it's a mock so you should do real integration tests as well, but for checking application logic this runs much faster than something requiring a browser, even a headless one.