Running jest test with coverage in typescript create-react-app (v2.1) throws super constructor error

🐛 Bug Report

When running jest tests with coverage enabled in a create-react-app react project (v2.1, which uses Babel 7 I believe) that contains typescript classes using inheritance (extends), this error is thrown:

ReferenceError: Must call super constructor in derived class before accessing 'this' or returning from derived constructor

       8 | class Derived extends Base {
    >  9 |   constructor(public anotherCount: number) {
         |                                            ^
      10 |     super();
      11 |   }

Running the tests without the --coverage option works fine.

To Reproduce

Create a new react app with typescript support (create-react-app v2.1 or higher required):

npx create-create-app jest-test --typescript

Add a new test file named “classes.tsx” to the src/ folder containing this code:

class Base {
  public counter: number = 0;
  increment() {
  
  }
}

class Derived extends Base {
  constructor(public anotherCount: number) {
    super();
  }
}

export { Base, Derived };

Edit the existing src/App.test.tsx file, adding this import:

import { Base, Derived } from "./classes";

… and this extra test:

it('coverage trigger', () => {
  const derivedInstance = new Derived(1);
  derivedInstance.increment();
});

Edit package.json and add a new script below “scripts” to run tests with coverage:

"test:coverage": "react-scripts test --coverage"

From a command line in the project directory, run npm run test:coverage

Expected behavior

The tests should complete without error with the --coverage option enabled.

Link to repl or repo (highly encouraged)

https://github.com/rsuk/repros/tree/master/jest-typescript-coverage-issue

Run npx envinfo --preset jest

Paste the results here:

  System:
    OS: Windows 10
    CPU: (12) x64 Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz
  Binaries:
    npm: 5.6.0 - C:\Program Files\nodejs\npm.CMD

[Joshproxy]

From the original error, I believe you can fix this by removing the parameter property.

8 | class Derived extends Base {
    >  9 |   constructor(public anotherCount: number) {
         |                                            ^
      10 |     super();
      11 |   }

Do this instead:

class Derived extends Base {
    constructor(anotherCount: number) {    
        super();
        this.anotherCount = anotherCount;
    }

[github-actions[bot]]

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