(core): Can't mock Stack with jest

When attempting to mock Stack with jest, a TypeError “Class extends value undefined is not a constructor or null” is thrown. I need to be able to mock the stack to test that the an inheriting class is calling super() parameters correctly.

Reproduction Steps

import { Stack } from "@aws-cdk/core";
import "@aws-cdk/assert/jest"; // <-- tried with and without this line

test("Can mock stack", () => {
  console.log(Stack);
});

jest.mock("@aws-cdk/core");

What did you expect to happen?

When I ran jest test I expected it not to fail with error. Ultimately it will be a call to an inheriting class type which calls the Stack mock. I’m able to do this with other classes such as Bucket.

What actually happened?

TypeError: Class extends value undefined is not a constructor or null

    > 1 | import { Stack } from "@aws-cdk/core"; (Line 1:1)

Environment

• CDK CLI Version : 1.89.0
• Framework Version: 1.89.0
• Node.js Version: 14.15.5
• OS : Windows 10.1909
• Language (Version): Typescript 4.1.4

Other

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This is 🐛 Bug Report

[martzcodes]

🤔 hm… yeah i had a typo when i did that last night: jest.mock("aws-cdk/aws-s3"); should’ve been jest.mock("@aws-cdk/aws-s3"); which DOES pass… interesting

import { Bucket } from '@aws-cdk/aws-s3';
jest.mock("@aws-cdk/aws-s3");
const mockBucket = (Bucket as unknown) as jest.Mock<Stack>;

class ExtendedBucket extends Bucket {
  constructor(scope: Construct, id: string) {
    super(scope, id);
  }
}

test("Calls super with correct params", () => {
    const app = new App();
    // when
    new ExtendedBucket(app, `Temp Bucket`);
    // then
    expect(mockBucket).toHaveBeenCalledWith(app, "Temp Bucket");
    expect(mockBucket).toBeCalledTimes(1);
  });

Very interesting… I’d never tried that before. I’m interested to hear what the cdk team says about it.

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