Sinon cannot stub non-existent own property 'function'

Question

I am trying to mock a module Database so that its getRecordDetails() member function would always return some fixed data. See below:

handler.js

const sinon = require("sinon");
const Database = require("../../lib/Database");
const database= new Database();

module.exports = {
  handler(event, context, callback) {
    event.Records.forEach(record=> {
       const recordDetails = database.getRecordDetails(record);
       // Do something with recordDetails
    });
  }
}
..

test.js

const sinon = require("sinon");
const db= require("../../lib/Database");
const lamdbda = require("../../lib/lambda.js");

describe("Test suite", () => {
  it("invoke lambda",  done => {
    lambda.handler(data, {}, (err, data) => {
      sinon.stub(db, "getRecordDetails").withArgs(sinon.match.any).returns("{id: 1}");
      ...
    }
  }

}

database.js

class Database {
  constructor() {
    this.dynamdbClient = new AWS.DynamoDB.DocumentClient();
  }

  getRecordDetails(record) {
    const param = {
      TableName: ..
      Key: {
        uuid: record.uuid
        ...
     }
    }
    const dbRecord = await docClient.get(params).promise();
    return mapToRecordDetails(dbRecord); // new object mostly 1-1 mappings.
  }

}

But I get:

TypeError: Cannot stub non-existent own property getRecordDetails What am I doing wrong?

Answer 1

The getRecordDetails method is an instance method of your Database class. Try sinon.stub(Database.prototype, 'getRecordDetails').

E.g.

handle.js:

const Database = require('./database');
const database = new Database();

module.exports = {
  handler(event, context, callback) {
    event.Records.forEach((record) => {
      const recordDetails = database.getRecordDetails(record);
      console.log(" ~ file: handler.js:8 ~ event.Records.forEach ~ recordDetails:", recordDetails)
    });
  },
};

database.js:

const AWS = require('aws-sdk');

class Database {
  constructor() {
    this.dynamdbClient = new AWS.DynamoDB.DocumentClient();
  }

  async getRecordDetails(record) {
    const param = {
      TableName: 'a',
      Key: {
        uuid: record.uuid,
      },
    };
    return docClient.get(params).promise();
  }
}

module.exports = Database;

handler.test.js:

const sinon = require('sinon');
const Database = require('./database');
const lamdbda = require('./handler.js');

describe('Test suite', () => {
  it('invoke lambda', () => {
    sinon.stub(Database.prototype, 'getRecordDetails').returns('{id: 1}');
    lamdbda.handler({ Records: [1] }, {}, (err, data) => {});
  });
});

Test result:

  Test suite
 ~ file: handler.js:8 ~ event.Records.forEach ~ recordDetails: {id: 1}
    ✓ invoke lambda


  1 passing (4ms)