Provide a `testInstance.context` property to facilitate context testing

[jsmrcaga]

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

What is the current behavior?
testInstance provides a props property, but does not provide a context property allowing for context tests.

What is the expected behavior?
testInstance.context should return an object containing the instance's current context

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?
At least 16.4.1

[jsmrcaga]

For what I have read on the source code, this could be enabled from ReactFiber.js and ReactTestRenderer.js

[gaearon]

Do you mean legacy context? I don't think we want to add more APIs supporting it given that the new context API fully supersedes it.

It's not clear to me how your suggestion would work with new context API. There's no single particular context. If a component reads some context and uses it, I think you should test how that component uses it. You don't need to test whether the context itself "works" — that's something we already test for inside React.

[jsmrcaga]

Hey @gaearon thanks for the quick answer!
My use case is that i have built a provider and a wrapper around pre-built components. I would like to test that the provider actually passes the context to the wrapped components, for example:

const component = renderer.create(
	<ThemeProvider theme={someTheme}>
		<Button name="someButton">Some Text!</Button>
	</ThemeProvider>
);

let button = component.root.findByType(Button);
expect(button.context).toHaveProperty('theme');

For now my solution has been to transform the theme context into a prop inside the wrapper.

[gaearon]

It sounds like you're really testing React here. There's no need to do it. We have plenty of tests for context. :-)

If you want to verify that Button does something with context, you can do this by testing Button output (presumably it uses context somehow).

[jsmrcaga]

Hmm I see your point. I was trying to test my implementation of Provider + wrapper, but as a matter of fact it is essentially a React test.