refactor: dedupe provider usage fetch logic and tests

src/test-utils/provider-usage-fetch.ts

@@ -0,0 +1,27 @@
+import { vi } from "vitest";
+import { withFetchPreconnect } from "./fetch-mock.js";
+
+type UsageFetchInput = string | Request | URL;
+type UsageFetchHandler = (url: string, init?: RequestInit) => Promise<Response> | Response;
+type UsageFetchMock = ReturnType<
+  typeof vi.fn<(input: UsageFetchInput, init?: RequestInit) => Promise<Response>>
+>;
+
+export function makeResponse(status: number, body: unknown): Response {
+  const payload = typeof body === "string" ? body : JSON.stringify(body);
+  const headers = typeof body === "string" ? undefined : { "Content-Type": "application/json" };
+  return new Response(payload, { status, headers });
+}
+
+export function toRequestUrl(input: UsageFetchInput): string {
+  return typeof input === "string" ? input : input instanceof URL ? input.toString() : input.url;
+}
+
+export function createProviderUsageFetch(
+  handler: UsageFetchHandler,
+): typeof fetch & UsageFetchMock {
+  const mockFetch = vi.fn(async (input: UsageFetchInput, init?: RequestInit) =>
+    handler(toRequestUrl(input), init),
+  );
+  return withFetchPreconnect(mockFetch) as typeof fetch & UsageFetchMock;
+}