error thrown within Jest unit test

I have a Jest unit test throwing an error when testing the creation of a bar chart. The call stack is as follows:

```
console.error
Failed to fetch scripts or layout. Cannot read property 'includes' of undefined
at CustomConsole.Object..console.error (../../node_modules/react-native/Libraries/LogBox/LogBox.js:33:14)
at registerError (../../node_modules/react-native/Libraries/YellowBox/YellowBox.js:169:7)
at errorImpl (../../node_modules/react-native/Libraries/YellowBox/YellowBox.js:84:22)
at CustomConsole.error (../../node_modules/react-native/Libraries/YellowBox/YellowBox.js:63:14)
at _callee$ (../../node_modules/@highcharts/highcharts-react-native/src/HighchartsReactNative.js:47:21)
at tryCatch (../../node_modules/regenerator-runtime/runtime.js:63:40)
at Generator.invoke [as _invoke] (../../node_modules/regenerator-runtime/runtime.js:293:22)
```

I have traced it in the HighchartsReactNative.js file to setHcAssets(), calling this.setLayout(), calling this.getAssetAsString() and the following code:

```
const downloadedModules = await FileSystem.readDirectoryAsync(FileSystem.cacheDirectory)
let fileName = 'ExponentAsset-' + asset.hash + '.' + asset.type
if (!downloadedModules.includes(fileName)) {
await asset.downloadAsync()
}
```

Seems like FileSystem react-native-unimodules is mocked, and has no cacheDirectory?

I tried the following

```
if (downloadedModules && !downloadedModules.includes(fileName)) {
```

But am now getting:

```
console.error
Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in the componentWillUnmount method.
in HighchartsReactNative (created by BarHighcharts)
```

For the unit test, I'm using @testing-library/react-native.

Anyway, I thought you should know. If this is an error on my part, please advise.