How to stub dependency injection class with Sinon.js? - node.js

Question

I have a class named ReportHandler that depends on other classes (ReportService, S3Handlere) like this one:
S3Handler: a class for downloading, uploading file to S3
ReportService: Doing CRUD to database
handleReportAsync is a function that download file from S3, do some logic and update file to database.
export class ReportHandler {
private s3Handler;
private reportService;
public constructor(reportService) {
this.reportService = reportService;;
const accessKey = process.env.AWS_ACCESS_KEY;
const secretKey = process.env.AWS_SECRET_ACCESS_KEY;
const bucketName = process.env.AWS_BUCKET_NAME;
this.s3Handler = new S3Handler(accessKey, secretKey, bucketName);
}
public async handleReportAsync(report) {
try {
const data = await this.s3Handler.downloadFile(report.id);
// do some logic
reportService.updateFile(report.id, data.Body);
} catch (error) {
}
}
}
I want to test whether the reportService.updateFile() is called or not, so I'm going to use spy for this task.
And obviously, I don't want to download real file from S3 so, How can I stub the this.s3Handler.downloadFile() function by Sinon.js.
This is my try but without success.
describe("ReportHandler", () => {
describe("handleReportAsync", () => {
let sandbox;
beforeEach(() => {
sandbox = Sinon.createSandbox();
});
afterEach(() => {
sandbox.restore();
});
it("should call updateFile() function", async () => {
const report = new Report(faker.random.uuid());
sandbox.stub(S3Handler.prototype, "downloadFile").callsFake(
(id) => {},
);
sandbox.stub(ReportService.prototype, "updateFile").callsFake(
(id, file) => {},
);
const reportHandler = new ReportHandler(new ReportService());
const spy = Sinon.spy(ReportService.prototype, "updateFile");
await reportHandler.handleReportAsync(report);
expect(spy.called).to.be.true;
});
});
});
Any advice is welcome! Thanks in advance.

Answer 1

Here is the unit test solution:
reportHandler.ts:
import S3Handler from "./s3Handler";
export class ReportHandler {
private s3Handler;
private reportService;
public constructor(reportService) {
this.reportService = reportService;
const accessKey = process.env.AWS_ACCESS_KEY;
const secretKey = process.env.AWS_SECRET_ACCESS_KEY;
const bucketName = process.env.AWS_BUCKET_NAME;
this.s3Handler = new S3Handler(accessKey, secretKey, bucketName);
}
public async handleReportAsync(report) {
try {
const data = await this.s3Handler.downloadFile(report.id);
this.reportService.updateFile(report.id, data.Body);
} catch (error) {}
}
}
s3Handler.ts:
export default class S3Handler {
constructor(accessKey, secretKey, bucketName) {}
}
reportHandler.test.ts:
import { ReportHandler } from "./reportHandler";
import sinon from "sinon";
describe("59766312", () => {
let sandbox;
beforeEach(() => {
sandbox = sinon.createSandbox();
});
afterEach(() => {
sandbox.restore();
});
describe("#handleReportAsync", () => {
it("should update file", async () => {
const reportServiceStub = { updateFile: sandbox.stub() };
const s3Handler = require("./s3Handler");
const downloadFileStub = sandbox.stub().resolves({ Body: "a" });
const s3HandlerInstanceStub = { downloadFile: downloadFileStub };
const s3HandlerStub = sandbox.stub(s3Handler, "default").callsFake(() => s3HandlerInstanceStub);
const reportHandler = new ReportHandler(reportServiceStub);
const report = { id: 1 };
await reportHandler.handleReportAsync(report);
sandbox.assert.calledOnce(s3HandlerStub);
sandbox.assert.calledWithExactly(s3HandlerInstanceStub.downloadFile, 1);
sandbox.assert.calledWithExactly(reportServiceStub.updateFile, 1, "a");
});
});
});
Unit test results with coverage report:
59766312
#handleReportAsync
✓ should update file
1 passing (12ms)
-----------------------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
-----------------------|----------|----------|----------|----------|-------------------|
All files | 100 | 100 | 90.91 | 100 | |
reportHandler.test.ts | 100 | 100 | 100 | 100 | |
reportHandler.ts | 100 | 100 | 100 | 100 | |
s3Handler.ts | 100 | 100 | 50 | 100 | |
-----------------------|----------|----------|----------|----------|-------------------|
Source code: https://github.com/mrdulin/mocha-chai-sinon-codelab/tree/master/src/stackoverflow/59766312