One React testing tip

Use an API mocking library. That’s it, it will make your life easier, you’ll be able to test everything without mocking basically anything and make Kent C. Dodds happy.

But we know that sometimes that’s not possible...

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Let’s say we have this:

// App.js
function App(){
    return (
        <ContextProvider>
            <MainComponent />       
        </ContextProvider>
    )
}

// Context stuff omitted

// MainComponent.js
function MainComponent(){
    const contextValue = useContext();

    return (
        <div>
            {contextValue}
        </div>
    )
}

You probably saw, made, and/or had to test something like this.

And it might be as easy as just wrapping your testing “render” in the context provider or testing it indirectly, by never unit testing MainComponent.

But what if you really want/need to unit test MainComponent?

You certainly can think of a few ways to test it, but I’ll be offering one way that needs only a small refactor and that gives your unit testing superpowers.

// MainComponent.js
function MainComponent({
    contextValue = useContext();
} = {}){
    return (
        <div>
            {contextValue}
        </div>
    )
}

That’s it!

You just put the useContext as a default parameter in MainComponent and in your tests you just:

render(
    <MainComponent contextValue={/* anything you want */} />
)

This makes testing trivial. (and if the context fetch something, then no mocking is required... yay!)

And if you have more levels of components above MainComponent, then you can always mock MainComponent:

// check your test framework, it’s pretty easy to do, just return something like:
const MockComponent = ({inputs, needed}) => {
    return (
        <div>
            <div>{something}</div>
            <div>{youWant}</div>
            <div>{toCheck}</div>
        </div>
    )
}

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But before using it, remember: if you can, first made the code easier to test!

If you can’t, or if you’re playing with untested legacy code... then: Tests are better than no tests.

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Cover Photo by Girl with red hat on Unsplash