Jest & AWS.DynamoDB.DocumentClient mocking - amazon-web-services

Question

I'm trying to mock a call to AWS.DynamoDB.DocumentClient. I tried several solutions I found online, but I cannot get it to work.
This is my best effort so far:
import * as AWS from 'aws-sdk';
import * as dynamoDbUtils from '../../src/utils/dynamo-db.utils';
jest.mock("aws-sdk");
describe('dynamo-db.utils', () => {
describe('updateEntity', () => {
it('Should return', async () => {
AWS.DynamoDB.DocumentClient.prototype.update.mockImplementation((_, cb) => {
cb(null, user);
});
await dynamoDbUtils.updateEntity('tableName', 'id', 2000);
});
});
});
I get error message
Property 'mockImplementation' does not exist on type '(params: UpdateItemInput, callback?: (err: AWSError, data: UpdateItemOutput) => void) => Request<UpdateItemOutput, AWSError>'.ts(2339)
My source file:
import AWS from 'aws-sdk';
let db: AWS.DynamoDB.DocumentClient;
export function init() {
db = new AWS.DynamoDB.DocumentClient({
region: ('region')
});
}
export async function updateEntity(tableName: string, id: string, totalNumberOfCharacters: number): Promise<AWS.DynamoDB.UpdateItemOutput> {
try {
const params = {
TableName: tableName,
Key: { 'id': id },
UpdateExpression: 'set totalNumberOfCharacters = :totalNumberOfCharacters',
ExpressionAttributeValues: {
':totalNumberOfCharacters': totalNumberOfCharacters
},
ReturnValues: 'UPDATED_NEW'
};
const updatedItem = await db.update(params).promise();
return updatedItem;
} catch (err) {
throw err;
}
}
Please advise how can I properly mock the response of AWS.DynamoDB.DocumentClient.update

Answer 1

Have some way to do the that thing (I think so).
This is one of them:
You use AWS.DynamoDB.DocumentClient, then we will mock AWS object to return an object with DocumentClient is mocked object.
jest.mock("aws-sdk", () => {
return {
DynamoDB: {
DocumentClient: jest.fn(),
},
};
});
Now, AWS.DynamoDB.DocumentClient is mocked obj. Usage of update function like update(params).promise() => Call with params, returns an "object" with promise is a function, promise() returns a Promise. Do step by step.
updateMocked = jest.fn();
updatePromiseMocked = jest.fn();
updateMocked.mockReturnValue({
promise: updatePromiseMocked,
});
mocked(AWS.DynamoDB.DocumentClient).mockImplementation(() => {
return { update: updateMocked } as unknown as AWS.DynamoDB.DocumentClient;
});
mocked import from ts-jest/utils, updateMocked to check the update will be call or not, updatePromiseMocked to control result of update function (success/ throw error).
Complete example:
import * as AWS from 'aws-sdk';
import * as dynamoDbUtils from './index';
import { mocked } from 'ts-jest/utils'
jest.mock("aws-sdk", () => {
return {
DynamoDB: {
DocumentClient: jest.fn(),
},
};
});
describe('dynamo-db.utils', () => {
describe('updateEntity', () => {
let updateMocked: jest.Mock;
let updatePromiseMocked: jest.Mock;
beforeEach(() => {
updateMocked = jest.fn();
updatePromiseMocked = jest.fn();
updateMocked.mockReturnValue({
promise: updatePromiseMocked,
});
mocked(AWS.DynamoDB.DocumentClient).mockImplementation(() => {
return { update: updateMocked } as unknown as AWS.DynamoDB.DocumentClient;
});
dynamoDbUtils.init();
});
it('Should request to Dynamodb with correct param and forward result from Dynamodb', async () => {
const totalNumberOfCharacters = 2000;
const id = 'id';
const tableName = 'tableName';
const updatedItem = {};
const params = {
TableName: tableName,
Key: { 'id': id },
UpdateExpression: 'set totalNumberOfCharacters = :totalNumberOfCharacters',
ExpressionAttributeValues: {
':totalNumberOfCharacters': totalNumberOfCharacters
},
ReturnValues: 'UPDATED_NEW'
};
updatePromiseMocked.mockResolvedValue(updatedItem);
const result = await dynamoDbUtils.updateEntity(tableName, id, totalNumberOfCharacters);
expect(result).toEqual(updatedItem);
expect(updateMocked).toHaveBeenCalledWith(params);
});
});
});