How to mock the response for below code using sinon , mocha chai

Question

Can anyone help me in writing one sample test scenarios?

storage is a library (google Cloud) finally below the line of code will return me an array consist of filename and Date.

function abc(){
   const files = [];
   files = await storage.bucket(bucketName).getFiles();
   return files;
}

Answer 1

Here is the unit test solution:

index.ts:

import { Storage } from "@google-cloud/storage";
const storage = new Storage();

export async function abc() {
  const bucketName = "xxx-dev";
  const files = await storage.bucket(bucketName).getFiles();
  return files;
}

export async function xyz(res) {
  const bucketName = "xxx-dev";
  return storage
    .bucket(bucketName)
    .file(res.fileName)
    .createReadStream();
}

index.spec.ts:

import { abc, xyz } from "./";
import { Storage } from "@google-cloud/storage";
import sinon from "sinon";
import { expect } from "chai";

describe("59373281", () => {
  afterEach(() => {
    sinon.restore();
  });
  it("abc should pass", async () => {
    const getFilesStub = sinon.stub().resolves(["file1", "file2"]);
    const bucketStub = sinon.stub(Storage.prototype, "bucket").callsFake(() => {
      return { getFiles: getFilesStub } as any;
    });
    const actual = await abc();
    expect(actual).to.be.deep.eq(["file1", "file2"]);
    sinon.assert.calledWith(bucketStub, "xxx-dev");
    sinon.assert.calledOnce(getFilesStub);
  });

  it("xyz should pass", async () => {
    const fileStub = sinon.stub().returnsThis();
    const createReadStreamStub = sinon.stub();
    const bucketStub = sinon.stub(Storage.prototype, "bucket").callsFake(() => {
      return {
        file: fileStub,
        createReadStream: createReadStreamStub,
      } as any;
    });
    const mRes = { fileName: "jestjs.pdf" };
    await xyz(mRes);
    sinon.assert.calledWith(bucketStub, "xxx-dev");
    sinon.assert.calledWith(fileStub, "jestjs.pdf");
    sinon.assert.calledOnce(createReadStreamStub);
  });
});

Unit test result with 100% coverage:

  59373281
    ✓ abc should pass
    ✓ xyz should pass


  2 passing (46ms)

---------------|----------|----------|----------|----------|-------------------|
File           |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
---------------|----------|----------|----------|----------|-------------------|
All files      |      100 |      100 |      100 |      100 |                   |
 index.spec.ts |      100 |      100 |      100 |      100 |                   |
 index.ts      |      100 |      100 |      100 |      100 |                   |
---------------|----------|----------|----------|----------|-------------------|

package versions:

"@google-cloud/storage": "^4.1.3",
"sinon": "^7.5.0",
"mocha": "^6.2.2",
"chai": "^4.2.0",

Source code: https://github.com/mrdulin/mocha-chai-sinon-codelab/tree/master/src/stackoverflow/59373281