import { Lambda } from 'aws-sdk';

export default class Service {
    public async callLambda(): Promise<void> {
        const lambda = new Lambda();
        const params: Lambda.Types.InvocationRequest = {
            FunctionName: `function-name`,
            InvocationType: 'Event',
        };
        await lambda.invoke(params).promise();
    }
}

import Service from '../../../../src/api/services/Service';

const fakePromise = {
    promise: jest.fn(),
};

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

describe('callLambda', () => {

    it('should return something... ', async done => {
        const service = new Service();
        const result = await service.callLambda();
        expect(result).toBeUndefined();
        done();
    });

    it('should throw an error... ', async done => {
        // modifying the implementation before call the function
        fakePromise.promise = jest.fn()
            .mockImplementation(() => Promise.reject(new Error()));

        try {
            const service = new Service();
            const result = await service.callLambda();
            expect(result).toBeUndefined();
        } catch (error) {
            expect(error).toBeDefined();
        }
        done();
    });
});

import { Lambda } from 'aws-sdk';
import Service from '../../../../src/api/services/Service';

// removing the factory function of the first way
jest.mock('aws-sdk');

describe('callLambda', () => {
    // moving the fake to inside our describe test
    // because we don't need it in jest.mock
    const fakePromise = {
        promise: jest.fn(),
    };

    beforeEach(() => {
        // adding the implementation before each test
        (Lambda as any).mockImplementation(() => {
            return {
                invoke: () => fakePromise,
            };
        });
    });

    it('should return something... ', async done => {
        const service = new Service();
        const result = await service.callLambda();
        expect(result).toBeUndefined();
        done();
    });

    it('should throw an error... ', async done => {
        // modifying the implementation before call the function
        fakePromise.promise = jest.fn()
            .mockImplementation(() => Promise.reject(new Error()));

        try {
            const service = new Service();
            const result = await service.callLambda();
            expect(result).toBeUndefined();
        } catch (error) {
            expect(error).toBeDefined();
        }
        done();
    });
});