AWS Mock not able to mock Lambda invoke()

Question

I am trying to mock an Lambda.invoke() call in my Jest. However, the mock call didn't work and instead executed the real invoke() method which leads to not authorized to perform: lambda:InvokeFunction. I couldn't find out what's wrong as I did the same for mocking DynamoDB.DocumentClient and it works without any issue.

Jest File:

describe('Mock Lambda', () => {

    beforeAll(async () => {
        AWSMock.mock('Lambda', 'invoke', (params, callback) => {
            if (params.FunctionName === 'MyLambaInvocation') {
                callback(null, { status: 200, data: { code: '0', message: 'Successful' }
            } 
        });

        const result = await (myTest.handler(event, context(), null) as Promise<APIGatewayProxyResult>);
    });

Typescript File:

import { Lambda } from 'aws-sdk';

export function invokeLambda(eventObject) {
    return new Promise<any>((resolve, reject) => {
        const lambdaConfig = {
            region: 'ap-southeast-1',
            endpoint: process.env.IS_OFFLINE ? 'http://localhost:8080' : undefined
        };

        const lambda = new Lambda(lambdaConfig);

        const params = {
            FunctionName: 'MyLambaInvocation',
            Payload: JSON.stringify(eventObject)
        };

        lambda.invoke(params, (error, result) => {
            if (error) {
                reject(error);
            } else {
                resolve(result);
            }
        });
    });
}

score 3 · Answer 1 · answered Mar 20 '20 at 06:35

Here is an example only using jestjs to mock.

index.ts:

import { Lambda } from 'aws-sdk';

export function invokeLambda(eventObject) {
  return new Promise<any>((resolve, reject) => {
    const lambdaConfig = {
      region: 'ap-southeast-1',
      endpoint: process.env.IS_OFFLINE ? 'http://localhost:8080' : undefined,
    };

    const lambda = new Lambda(lambdaConfig);

    const params = {
      FunctionName: 'MyLambaInvocation',
      Payload: JSON.stringify(eventObject),
    };

    lambda.invoke(params, (error, result) => {
      if (error) {
        reject(error);
      } else {
        resolve(result);
      }
    });
  });
}

index.test.ts:

import { invokeLambda } from './';
import { Lambda as LambdaMock } from 'aws-sdk';

jest.mock('aws-sdk', () => {
  const mLambda = { invoke: jest.fn() };
  return { Lambda: jest.fn(() => mLambda) };
});

describe('Mock Lambda', () => {
  it('should invoke lambda', async () => {
    const mLambda = new LambdaMock();
    const mResult = {};
    (mLambda.invoke as jest.Mocked<any>).mockImplementationOnce((params, callback) => {
      callback(null, mResult);
    });
    const actual = await invokeLambda({});
    expect(actual).toEqual({});
    expect(LambdaMock).toBeCalledWith({ region: 'ap-southeast-1', endpoint: undefined });
    expect(mLambda.invoke).toBeCalledWith(
      {
        FunctionName: 'MyLambaInvocation',
        Payload: JSON.stringify({}),
      },
      expect.any(Function),
    );
  });

  it('should handle error if invoke failure', async () => {
    const mLambda = new LambdaMock();
    const mError = new Error('network');
    (mLambda.invoke as jest.Mocked<any>).mockImplementationOnce((params, callback) => {
      callback(mError);
    });
    await expect(invokeLambda({})).rejects.toThrow('network');
    expect(LambdaMock).toBeCalledWith({ region: 'ap-southeast-1', endpoint: undefined });
    expect(mLambda.invoke).toBeCalledWith(
      {
        FunctionName: 'MyLambaInvocation',
        Payload: JSON.stringify({}),
      },
      expect.any(Function),
    );
  });
});

unit test results with coverage report:

 PASS  stackoverflow/60753252/index.test.ts
  Mock Lambda
    ✓ should invoke lambda (8ms)
    ✓ should handle error if invoke failure (3ms)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |     100 |       75 |     100 |     100 |                   
 index.ts |     100 |       75 |     100 |     100 | 7                 
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        4.054s, estimated 11s

source code: https://github.com/mrdulin/react-apollo-graphql-starter-kit/tree/master/stackoverflow/60753252

AWS Mock not able to mock Lambda invoke()

1 Answers1