Mocking dynamodb scan using jest - node.js

Question

For the source code(dynamodb.js)：
const AWS = require("aws-sdk");
const Promise = require("bluebird");
const client = new AWS.DynamoDB.DocumentClient();
module.exports.db = (method, params) => {
console.log("access dynamodb ");
return Promise.fromCallback(cb => client[method](params, cb));
};
Using the test that looks like this(dont want't to mock Promise.fromCallback):
describe("test", () => {
const realAWS = require("aws-sdk");
let fakePromise;
let fakeDynamo;
let dbClient;
beforeAll(function() {
fakePromise = jest.fn();
fakeDynamo = {
get: (params, cb) => {
fakePromise(params, cb);
}
};
realAWS.DynamoDB.DocumentClient = jest.fn(() => fakeDynamo);
dbClient = require("../dynamodb");
});
test.only("Test successed", done => {
let result = dbClient.db("get", null);
console.log("access dynamodb ");
expect(fakePromise).toHaveBeenCalled();
});
});
but when tun the test ,the error was heppend:
Timeout - Async callback was not invoked within the 5000ms timeout specified by jest.setTimeout.
if anyone can help me? Thanks!

Answer 1

You need to mock the implementation of the client.get method as a node callback style. So that Promise.fromCallback method will covert callback style to a promise.
Besides, you need to trigger the callback in your test case. That's why you got a timeout error.
E.g.
dynamodb.js:
const AWS = require('aws-sdk');
const Promise = require('bluebird');
const client = new AWS.DynamoDB.DocumentClient();
module.exports.db = (method, params) => {
console.log('access dynamodb');
return Promise.fromCallback((cb) => client[method](params, cb));
};
dynamodb.test.js:
const { db } = require('./dynamodb');
const AWS = require('aws-sdk');
jest.mock('aws-sdk', () => {
const mClient = { get: jest.fn() };
const mDynamoDB = {
DocumentClient: jest.fn(() => mClient),
};
return { DynamoDB: mDynamoDB };
});
const mockClient = new AWS.DynamoDB.DocumentClient();
describe('54360588', () => {
afterAll(() => {
jest.resetAllMocks();
});
it('should pass', async () => {
mockClient.get.mockImplementationOnce((err, callback) => {
callback(null, 'fake data');
});
const actual = await db('get', null);
expect(actual).toBe('fake data');
expect(mockClient.get).toBeCalledWith(null, expect.any(Function));
});
});
unit test result with coverage report:
PASS src/stackoverflow/54360588/dynamodb.test.js (10.74s)
54360588
✓ should pass (28ms)
console.log src/stackoverflow/54360588/dynamodb.js:177
access dynamodb
-------------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
-------------|----------|----------|----------|----------|-------------------|
All files | 100 | 100 | 100 | 100 | |
dynamodb.js | 100 | 100 | 100 | 100 | |
-------------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 12.636s