As a minimal example:

import {readable, writable} from "svelte/store";

import {is_readable} from "svelte-commons/lib/util/shared";

const readable_store = readable("some value");
const writable_store = writable("some value");

console.log(
    is_readable(readable_store),
    is_readable(writable_store)
); // logs: `true`, `true`

As a minimal example:

import {readable, writable} from "svelte/store";

import {is_writable} from "svelte-commons/lib/util/shared";

const readable_store = readable("some value");
const writable_store = writable("some value");

console.log(
    is_writable(readable_store),
    is_writable(writable_store)
); // logs: `false`, `true`