# A Litany of Woes

# tl;dr:

I learned recently that the only way to use Enzyme to test a React component that relies on a useContext hook appears to be to use render or mount, not shallow.

# More details:

I've been helping some coworkers with thorny questions about testing React components lately, and found some surprising issues I hadn't seen blogged about elsewhere. Specifically, let's dive in to testing with the shallow render method from Enzyme.

Assumptions you can make for this post include:

  • I'm talking about React with hooks, so 16.8+
  • I'm talking about using the Adapter from Enzyme for testing
  • I've tested with mochapack and jest and gotten the same results
  • I am not an expert, nor a maintainer of any of the above libraries.
  • I do use React for work, and have a basic familiarity with React testing libraries.

# General Concerns about shallow

Famous JavaScript guy Kent C. Dodds says to never use shallow rendering, and he doesn't even mention the useContext weirdness I'm about to describe. He makes some great points; I recommend giving it a read.

# If I do use shallow, I still can use React.Context, right?

The docs for shallow imply that you can still use context in shallowly rendered components, by providing the wrappingComponent option. This is misleading.

options.wrappingComponent: (ComponentType [optional]): A component that will render as a parent of the node. It can be used to provide context to the node, among other things. See the getWrappingComponent() docs for an example. Note: wrappingComponent must render its children.
options.wrappingComponentProps: (Object [optional]): Initial props to pass to the wrappingComponent if it is specified.

The only way to test a component with Enzyme that relies on a useContext hook appears to be to use render or mount, not shallow.

I made a CodeSandbox of every method I could think of to potentially use useContext with shallow, all of which fail. (The tests that pass use mount or shallow or no Context at all.)

Later, I found this longstanding issue in the Enzyme repository describing this exact issue.

Here's a helpful comment from another user with suggested workarounds;
here's a maintainer confirming that fixing this would take substantial effort and probably won't happen.

# What about context from React-Redux?

You might think you can avoid this by using React-Redux as your context provider, instead of React's built-in context. You might think this is supported, since the code sample in the Enzyme docs for ShallowWrapper:getWrappingComponent show exactly this. You would be wrong, since React-Redux now also uses useContext for its operations. I have a test demonstrating this in my Code Sandbox repro. (Look for "can use a react-redux provider"). (h/t to coworker Greg, who separately stumbled on this problem this week, for pointing this out!)

I hope this post saves you time and frustration. (No fewer than 3 members of my team spent several hours each on this, just this week.) Happy testing!