testing/network.mjs

Functions

Imports

It imports no other module of this repo. Imported by testing/access.mjs, testing/github.mjs.

Source

1// The network guard every test layer writes for itself: a global fetch that refuses, and the swap underneath it.
2// No test framework is imported: the swap is a property definition, the same one vitest's stubGlobal makes, so it works in node and workerd.
3
4/**
5 * The URL a fetch was asked for, from any of the three shapes fetch accepts.
6 *
7 * @param {RequestInfo | URL} input
8 * @returns {string}
9 */
10export function urlOf(input) {
11  return typeof input === "string" ? input : input instanceof URL ? input.href : input.url;
12}
13
14/**
15 * Replaces `globalThis.fetch` with `impl` and returns the function that puts back what was there. Restores run in the
16 * reverse order of installs, as any stack of stubs does.
17 *
18 * @param {typeof fetch} impl
19 * @returns {() => void}
20 */
21export function installFetch(impl) {
22  const previous = Object.getOwnPropertyDescriptor(globalThis, "fetch");
23  Object.defineProperty(globalThis, "fetch", { value: impl, writable: true, configurable: true, enumerable: true });
24  return () => {
25    if (previous) Object.defineProperty(globalThis, "fetch", previous);
26    else delete (/** @type {{ fetch?: unknown }} */ (globalThis)).fetch;
27  };
28}
29
30/**
31 * Installs a fetch that throws an error naming the URL, so reaching the network is a failure and never a silent call.
32 * `hint` is appended to the message: where the layer's recorded stubs live. Returns the restore, so it can be a
33 * vitest `beforeEach` return value.
34 *
35 * @param {{ hint?: string }} [options]
36 * @returns {() => void}
37 */
38export function refuseNetwork({ hint } = {}) {
39  return installFetch(async (input) => {
40    throw new Error(
41      `this layer does not reach the network, and something asked for ${urlOf(input)}.` + (hint ? ` ${hint}` : ""),
42    );
43  });
44}