ReferenceError: Cannot access 'observer' before initialization

[dominikzogg]

• @testing-library/react version:
• react version: 16.13.1
• node version: 13.11.0
• npm (or yarn) version: 6.13.7

Relevant code or config:

https://github.com/chubbyphp/petstore-react/blob/master/src/__tests__/Component/Form/PetForm.test.tsx

What you did:

npm test -- --watchAll

What happened:

petstore-react/node_modules/@testing-library/dom/dist/wait-for.js:41
      (0, _helpers.setImmediate)(() => observer.disconnect());
                                                ^

ReferenceError: Cannot access 'observer' before initialization
    at Immediate.<anonymous> (/home/schreiner/Documents/webpages/petstore-react/node_modules/@testing-library/dom/dist/wait-for.js:41:49)
    at processImmediate (internal/timers.js:456:21)
/home/schreiner/Documents/webpages/petstore-react/node_modules/@testing-library/dom/dist/wait-for.js:41
      (0, _helpers.setImmediate)(() => observer.disconnect());                                                ^ReferenceError: Cannot access 'observer' before initialization    at Immediate.<anonymous> (/home/schreiner/Documents/webpages/petstore-react/node_modules/@testing-library/dom/dist/wait-for.js:41:49)    at processImmediate (internal/timers.js:456:21)

TypeError: MutationObserver is not a constructor

      214 |     fireEvent.click(getByTestId('submit-pet'));
      215 | 
    > 216 |     await waitForElement(() =>
          |           ^
      217 |         getByTestId('submit-pet')
      218 |     );

Reproduction:

Run tests on: https://github.com/chubbyphp/petstore-react

Problem description:

This problem apears when upgrading to 10., worked well on 9.

Suggested solution:

[pushred]

@dominikzogg looks like testing-library/dom-testing-library#477 is discussing this issue with different resolution options

[dominikzogg]

@pushred thanks, adding jest-environment-jsdom-sixteen solved the issue