🐛 returns a rejected promise if the message ID is already reserved

Author: Milly

session.ts

@@ -92,7 +92,12 @@ export class Session {
       return Promise.reject(new Error("Session is not running"));
     }
     const { reservator } = this.#running;
-    return reservator.reserve(msgid);
+    try {
+      // NOTE: It throws an error instead returns a rejected promise.
+      return reservator.reserve(msgid);
+    } catch (err) {
+      return Promise.reject(err);
+    }
   }
 
   /**

session_test.ts

@@ -12,6 +12,7 @@ import {
   pop,
   push,
 } from "https://deno.land/x/[email protected]/mod.ts";
+import { AlreadyReservedError } from "https://deno.land/x/[email protected]/errors.ts";
 import { buildRedrawCommand } from "./command.ts";
 import { buildMessage, Message } from "./message.ts";
 import { Session } from "./session.ts";
@@ -99,6 +100,21 @@ Deno.test("Session.recv", async (t) => {
     },
   );
 
+  await t.step(
+    "rejects an error if the message ID is already reserved",
+    async () => {
+      const { session } = createDummySession();
+
+      session.start();
+      session.recv(-1);
+
+      await assertRejects(
+        () => session.recv(-1),
+        AlreadyReservedError,
+      );
+    },
+  );
+
   await t.step(
     "waits a command response message and resolves with it",
     async () => {