react-test-renderer: the findByType method doesn't work with memo components

[bensampaio]

Do you want to request a feature or report a bug?
Feature

What is the current behavior?
Whenever I try something like:

ReactTestRenderer.create(<SomeComponent />).root.findByType(SomeMemoComponent);

I get the following error: No instances found with node type: "undefined". The only way I found for this to work was to reference the type property of memo components like this:

ReactTestRenderer.create(<SomeComponent />).root.findByType(SomeMemoComponent.type);

I am fine with this solution but then flow complains that type doesn't exist so I find myself fixing this with $FlowFixMe all over the place.

What is the expected behavior?

I would expect that passing a memo component to findByType would work. Or that flow would recognize the type property of memo components. I think both should work, specially the first option.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?

No, it never worked as far as I know.

[threepointone]

I think this is a bug, likely fixed by #17278

[milesj]

If you debug the result tree, the memo component does not exist, only the component that it wrapped. I believe this is by design? Since the tree is the "reconciled" tree. Would need to dig further.

Edit: Tested on v16.12. The PR above didn't fix this.

[bensampaio]

@milesj indeed, v16.12 didn't fix this problem. If findByType can't work with memo components then I would expect flow to at least recognize the type property of memo components.

[ianschmitz]

I've found a workaround for those that need it.

Pin react, react-dom, react-test-renderer to 16.11.0, and most importantly add a dependency to react-is@16.11.0.

[henryqdineen]

I am having the same issue. One thing that I found is that if SomeMemoComponent.defaultProps is defined it does work as expected. It looks like there is some distinction between MemoComponent and SimpleMemoComponent when building the tree.

[martijnsenden]

Also having this issue. @henryqdineen I tried defining the defaultProps, but that did not help for me.

[gaearon]

See my comment on #17700 (comment).

[chris-feist]

I ended up creating my own test predicate until this is resolved:

const MyComponent = () => (<div />);
const MemoMyComponent = React.memo(MyComponent);

const elementByType = (type) => (element) => (
  element.type === type // Match non-memo'd
  || element.type === type.type // Match memo'd
);

const rendered = renderer.create((
  <MyComponent />
));

rendered.root.find(elementByType(MyComponent)) 

const renderedWithMemo = renderer.create((
  <MemoMyComponent />
));

renderedWithMemo.root.find(elementByType(MemoMyComponent))