Intermittent error in @sheerun/mutationobserver-shim

[pelotom]

• DOM Testing Library version: 6.1.0
• node version: 11.15.0
• npm (or yarn) version: 1.17.3

Problem description:

I'm seeing this intermittent error in my tests:

TypeError: Cannot read property 'nodeType' of null

      at copy (node_modules/@sheerun/mutationobserver-shim/MutationObserver.js:504:45)
      at clone (node_modules/@sheerun/mutationobserver-shim/MutationObserver.js:533:11)
      at createMutationSearcher (node_modules/@sheerun/mutationobserver-shim/MutationObserver.js:178:25)
      at MutationObserver.observe (node_modules/@sheerun/mutationobserver-shim/MutationObserver.js:110:21)
      at Promise (node_modules/@testing-library/dom/dist/wait-for-element.js:31:14)
      at waitForElement (node_modules/@testing-library/dom/dist/wait-for-element.js:22:10)
      at asyncWrapper (node_modules/@testing-library/dom/dist/wait-for-element.js:67:54)
      at node_modules/@testing-library/react/dist/pure.js:51:22
      at batchedUpdates$1 (node_modules/react-dom/cjs/react-dom.development.js:21643:12)
      at act (node_modules/react-dom/cjs/react-dom-test-utils.development.js:1002:14)
      at act (node_modules/react-dom/cjs/react-dom-test-utils.development.js:1418:12)
      at asyncAct (node_modules/@testing-library/react/dist/act-compat.js:118:12)

Unfortunately it's a heisenbug which only seems to reproduce (sometimes) when running the full suite of tests in our proprietary codebase.

[LaurensBosscher]

We're dealing with the same issue. What might help is upgrading to JSDom fifteen , this has support for mutation observers so you will not need the polyfill anymore :)

It's a though one to track down and debug so I cannot give you any guarantees that this will help but it seems to work for us.

[kentcdodds]

Hi there,

I'd recommend upgrading JSDOM and the issue will just magically fade away 😅 Even without this issue I think upgrading JSDOM is a good step anyway.