React Exceptionless Jest Mock (Jest doesn't yet support esm modules).

App.test.tsx

import { ClassAttributes, HTMLAttributes } from "react";

jest.mock("@exceptionless/react", () => {
  return {
    __esModule: true,
    Exceptionless: {
      startup: jest.fn()
    },
    ExceptionlessErrorBoundary: (props: JSX.IntrinsicAttributes & ClassAttributes<HTMLDivElement> & HTMLAttributes<HTMLDivElement>) => {
      return <div {...props} />;
    }
  };
});