Mocking a class in typescript with jest

Question

I am trying to unit test (with Jest) my handler module that makes use of a summary class.

My original summary class looks like:

import DynamoDBClient from './ddbClient/DynamoDBClient'
import { DynamoDB } from 'aws-sdk'
import { iSummaryReader, iObsSummariesAttributes } from './Summary.d'
import { JSONAPIResource } from '../JSONAPIResponse'

export default class Summary {
  reader: iSummaryReader

  constructor(reader: iSummaryReader) {
    this.reader = reader
  }


  getSummary = async (keyName: string, keyValue: string): Promise<JSONAPIResource<iObsSummariesAttributes>> => {
    return new Promise<JSONAPIResource<iObsSummariesAttributes>>((resolve, reject) => {
      const gettingItem = this.reader.getItem(keyName, keyValue)
      console.log(gettingItem)
      gettingItem.then((resp) => {
        resolve(resp)
      }).catch((err: Error) => {
        reject(err.message)
      })
    })
  }
}

In my handler module I import with import Summary from './lib/Summary' (Note: same line is used in handler.test.ts

Inside the handler function

try {
  const dynamodbObj: iSummaryReader = new DynamoDBClient(documentClient, someTable)
  const summary = new Summary(dynamodbObj)
  const data: JSONAPIResource<iObsSummariesAttributes> = await summary.getSummary('id', someID)
}

My results depend on my approach if try an automatic mock

jest.mock('./lib/Summary', () =>
{
  return {
    getSummary: jest.fn()
  }
})

I get the error

TypeError: Summary_1.default is not a constructor

If I create a manual mock under lib/__mocks__/Summary.ts with jest.mock('./lib/Summary') it does work until I get the point

expect(Summary).toHaveBeenCalledTimes(1)

Where it complains about me not being able to do this on summary. I also am unable to access my method to test that they are being called this way.

Note: My hanlder is for a lambda function so I am unable to inject the class that way where I have successfully tested that I can mock an injected class.

EDIT

The tsconfig.json is:

{
  "compilerOptions": {
    "rootDir": "./src",
    "outDir": "./build",
    "declaration": false,
    "target": "es2015",
    "moduleResolution": "node",
    "module": "commonjs",
    "noImplicitReturns": true,
    "noImplicitThis": true,
    "strictNullChecks": true,
    "alwaysStrict": true,
    "lib": [
      "dom",
      "es2015.promise",
      "es2017.object",
      "es2016"
    ],
  },
  "include": [
    "src/**/*.ts"
  ],
}

Answer 1

I do not know why this was failing, but I the following steps seem to work to fix it.

1. Change the class export from default

From

`export default class Summary {`

to

`class summary`

+ export = summary at the end

2. Use import = require to import it.

   import Summary = require('./lib/Summary')

Those two changes allowed it to find the jest.mock.