Add fetch example & test

[gnclmorais]

This is one of the situations I’ve used the most with ember-browser-services but I didn’t see it reflected on the documentation… So I whipped up an example and corresponding test to make it clearer for other users.

I ran into an interesting situation on the test, where the function was being bound and I had to think a bit outside the box. Let me know what you think!

[vitch]

Shouldn't the faked version match the signature of the original function?

e.g. shouldn't this return something matching:

interface Response extends Body {
    readonly headers: Headers;
    readonly ok: boolean;
    readonly redirected: boolean;
    readonly status: number;
    readonly statusText: string;
    readonly type: ResponseType;
    readonly url: string;
    clone(): Response;
}

interface Body {
    readonly body: ReadableStream<Uint8Array> | null;
    readonly bodyUsed: boolean;
    arrayBuffer(): Promise<ArrayBuffer>;
    blob(): Promise<Blob>;
    formData(): Promise<FormData>;
    json(): Promise<any>;
    text(): Promise<string>;
}

(from lib.dom)

Obviously you can't have the right body but the url on the Response would enable the test you've written (and maybe in general the sort of tests that you'd want to fake fetch for?)

[gnclmorais]

Yeah, we can make it match 👍 That’s definitely a great improvement! I went with a simple example here, but might as well go all the way and provide a correct example.

[NullVoxPopuli]

@gnclmorais if you need/want help, lemme know!

personally, I don't think we should block README updates on something like this, since the underlying implementation is basically YOLO-stubbing