Enable usage of `createContext` with independent `mount`

[brunnerh]

Describe the problem

@accuser made this observation here:

I like the simplicity of this approach, but it seems to take away the ability to pass context when mounting a component during testing. Or am I missing something obvious?

I used to do this:

mount(MyComponent, { props, context: { CONTEXT_TOKEN: mockContext }, target: document.body });

Now that the context key is opaque, I don't seem to have a way to do this.

Describe the proposed solution

Maybe the key should be exposed (e.g. on the setter) to enable something like:

mount(MyComponent, { context: { [setContext.key]: mockContext }, /* ... */ });

Or maybe a function for creating a context entry (key/value pair) could be provided, this way the type checking could still be automatically enforced:

mount(MyComponent, {
  context: new Map([
      setContext.entry(mockContext), // [{}, T]
      // ... other contexts, e.g. via `...Object.entries({ ... })`
  ]),
  // ...
});

Importance

would make my life easier