React Testing Library wrapper option

In the docs

The wrapper option lets you pass in a component to be wrapped around the given ui in a RTL render().

const RenderWrapper = ({ children }) => {
    return ( 
        <ThemeProvider theme="light">
            {children}
        </ThemeProvider>
    )
}

const customRender = (ui, options) => {
    return render(ui, { wrapper: RenderWrapper, ...options });
}

See Custom Render in the React Testing Library API docs

In the source

wrapper is passed in to the renderRoot function, it's renamed to WrapperComponent.

Which is then passed in to wrapUiIfNeeded as wrapperComponent

function wrapUiIfNeeded(innerElement, wrapperComponent) {
  return wrapperComponent
    ? React.createElement(wrapperComponent, null, innerElement)
    : innerElement
}