jest-fetch-mock-cache
Caching mock implementation for jest-fetch-mock.
Copyright (c) 2023 by Gadi Cohen. MIT Licensed.
Introduction
Instead of individually handcrafting a mock for each and every fetch()
call in your code, maybe you'd like to perform a real fetch() once,
cache the result, and use that cache result for future calls. Super
useful for TDD against existing APIs!!
Note: this is a brand new project. It works but you may want to wait
a little before any serious use. Feature requests welcome!
Quick Start
import fetchMock from "jest-fetch-mock";
fetchMock.enableMocks();
import { describe, expect, test as it } from "@jest/globals";
import createCachingMock from "jest-fetch-mock-cache";
// See list of possible stores, below.
import Store from "jest-fetch-mock-cache/lib/stores/nodeFs";
const cachingMock = createCachingMock({ store: new Store() });
describe("cachingMock", () => {
it("works with a JSON response", async () => {
const url = "http://echo.jsontest.com/key/value/one/two";
const expectedResponse = { one: "two", key: "value" };
for (let i = 0; i < 2; i++) {
// If you get a TypeError here, make sure @types/jest is instaled.
fetchMock.mockImplementationOnce(cachingMock);
const response = await fetch(url);
const data = await response.json();
const expectedCacheHeader = i === 0 ? "MISS" : "HIT";
expect(response.headers.get("X-JFMC-Cache")).toBe(expectedCacheHeader);
expect(data).toEqual(expectedResponse);
}
});
});
-
The first time this runs, a real request will be made to
jsontest.com, and the result returned. But, it will also be
saved to cache.
-
Subsequent requests will return the cached copy without
making an HTTP request.
Note: the package is designed to be used with jest-fetch-mock, but that's
not required. Since it's a complete impleemntation on its own, you could
do something like
// Do this and then use this `fetch()` function, or set global.fetch = ...
const fetch = jest.fn(createCachingMock({ store: new Store() }));
What's cached
Sample output from the Quick Start code above, when used with NodeFSStore:
$ cat tests/fixtures/http/echo.jsontest.com\!key\!value\!one\!two
{
"request": {
"url": "http://echo.jsontest.com/key/value/one/two"
},
"response": {
"ok": true,
"status": 200,
"statusText": "OK",
"headers": {
"access-control-allow-origin": "*",
"connection": "close",
"content-length": "39",
"content-type": "application/json",
"date": "Fri, 21 Jul 2023 16:59:17 GMT",
"server": "Google Frontend",
"x-cloud-trace-context": "344994371e51195ae21f236e5d7650c4"
},
"bodyJson": {
"one": "two",
"key": "value"
}
}
}
For non-JSON bodies, a bodyText is stored as a string. We store an
object as bodyJson for readability reasons.
Debugging
We use debug for debugging. E.g.:
$ DEBUG=jest-fetch-mock-cache:* yarn test
yarn run v1.22.19
$ jest
jest-fetch-mock-cache:core [jsmc] Fetching and caching 'http://echo.jsontest.com/key/value/one/two' +0ms
jest-fetch-mock-cache:core [jsmc] Using cached copy of 'http://echo.jsontest.com/key/value/one/two' +177ms
PASS src/index.spec.ts
cachingMock
✓ should work (180 ms)
Available Stores
import createCachingMock from "jest-fetch-mock-cache";
// Use Node's FS API to store as (creating paths as necessary)
// `${process.cwd()}/tests/fixtures/${filenamifyUrl(url)}`.
// https://github.com/sindresorhus/filenamify-url
import JFMCNodeFSStore from "./stores/nodeFs";
const fsCacheMock = createCachingMock({ store: new JFMCNodeFSStore() });
fetchMock.mockImplementationOnce(fsCacheMock);
// To override the store location, init with store with e.g.:
// new JFMCNodeFSStore({ location: "tests/other/location" })
// Keep in memory
import JSMCMemoryStore from "./stores/memory";
const memoryCacheMock = createCachingMock({ store: new JSMCMemoryStore() });
fetchMock.mockImplementationOnce(memoryCacheMock);
Create your own Store
import JFMCStore from "jest-fetch-mock-cache/lib/store";
import type { JFMCCacheContent } from "jest-fetch-mock-cache/lib/store";
import db from "./db"; // your existing db
class MyCustomStore extends JFMCStore {
async fetchContent(req: Request): Promise<JFMCCacheContent | undefined> {
const key = await this.idFromResponse(req);
return (await db.collection("jfmc").findOne(key)).content;
}
async storeContent(req: Request, content: JFMCCacheContent): Promise<void> {
const key = await this.idFromResponse(req);
await db.collection("jfmc").insertOne({ _id: key, content });
}
}
export default MyCustomStore;
TODO
