How to run Jest test on a asyn function - asynchronous

Question

I have a function that will find a zip file in the directory and unzip the file and it work fine. however, I'm wondering how i can run a test on this function using Jest.
var fs = require('fs'),
PNG = require('pngjs').PNG
const unzipper = require('unzipper')
PNG = require('pngjs').PNG
const dir = __dirname + "/";
function unzipFile(fileName, outputPath) {
return new Promise((resolve, reject) => {
if (fs.existsSync(fileName) !== true) {
reject("there is no zip file");
}
const createdFile = dir + fileName;
const stream = fs
.createReadStream(createdFile)
.pipe(unzipper.Extract({ path: outputPath }));
stream.on("finish", () => {
console.log("file unzipped");
resolve(outputPath);
});
});
}
I have read through the doc and try to use .then but I'm not sure how my expected output should be like when using Jest.

Answer 1

Here is the unit test solution:
index.js:
const fs = require("fs");
const unzipper = require("./unzipper");
const dir = __dirname + "/";
function unzipFile(fileName, outputPath) {
return new Promise((resolve, reject) => {
if (fs.existsSync(fileName) !== true) {
reject("there is no zip file");
}
const createdFile = dir + fileName;
const stream = fs
.createReadStream(createdFile)
.pipe(unzipper.Extract({ path: outputPath }));
stream.on("finish", () => {
console.log("file unzipped");
resolve(outputPath);
});
});
}
module.exports = unzipFile;
index.spec.js:
const unzipFile = require("./");
const fs = require("fs");
const unzipper = require("./unzipper");
jest.mock("fs", () => {
return {
existsSync: jest.fn(),
createReadStream: jest.fn().mockReturnThis(),
pipe: jest.fn()
};
});
describe("unzipFile", () => {
afterEach(() => {
jest.restoreAllMocks();
jest.resetAllMocks();
});
it("should unzip file correctly", async () => {
const filename = "go.pdf";
const outputPath = "workspace";
const eventHandlerMap = {};
const mStream = {
on: jest.fn().mockImplementation((event, handler) => {
eventHandlerMap[event] = handler;
})
};
const logSpy = jest.spyOn(console, "log");
fs.existsSync.mockReturnValueOnce(true);
fs.createReadStream().pipe.mockReturnValueOnce(mStream);
jest.spyOn(unzipper, "Extract").mockReturnValueOnce({});
const pending = unzipFile(filename, outputPath);
eventHandlerMap["finish"]();
const actual = await pending;
expect(actual).toEqual(outputPath);
expect(fs.existsSync).toBeCalledWith(filename);
expect(fs.createReadStream).toBeCalled();
expect(fs.createReadStream().pipe).toBeCalledWith({});
expect(logSpy).toBeCalledWith("file unzipped");
expect(mStream.on).toBeCalledWith("finish", eventHandlerMap["finish"]);
});
});
Unit test result with coverage report:
PASS src/stackoverflow/59027031/index.spec.js
unzipFile
✓ should unzip file correctly (10ms)
console.log node_modules/jest-mock/build/index.js:860
file unzipped
-------------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
-------------|----------|----------|----------|----------|-------------------|
All files | 92.31 | 50 | 75 | 92.31 | |
index.js | 91.67 | 50 | 100 | 91.67 | 8 |
unzipper.js | 100 | 100 | 0 | 100 | |
-------------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 5.618s, estimated 9s
Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/59027031