feat: implement command registration for booster role bot and add tests

src/discord/registerCommands.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, test } from "bun:test";
+import { registerGuildCommands, type DiscordRestClient } from "./registerCommands";
+
+class FakeRestClient implements DiscordRestClient {
+  route: string | null = null;
+  body: unknown = null;
+
+  async put(route: string, input: { body: unknown }): Promise<unknown> {
+    this.route = route;
+    this.body = input.body;
+    return null;
+  }
+}
+
+describe("registerGuildCommands", () => {
+  test("registers booster role command to the configured guild", async () => {
+    const rest = new FakeRestClient();
+
+    await registerGuildCommands(rest, { clientId: "client", guildId: "guild" });
+
+    expect(rest.route).toBe("/applications/client/guilds/guild/commands");
+    expect(rest.body).toEqual([
+      expect.objectContaining({ name: "booster-role", description: "Manage your cosmetic booster role" })
+    ]);
+  });
+});