diff --git a/functions/db/deck-access/get-deck-access-by-share-id-db.ts b/functions/db/deck-access/get-deck-access-by-share-id-db.ts
index d442eb14..38e60cd8 100644
--- a/functions/db/deck-access/get-deck-access-by-share-id-db.ts
+++ b/functions/db/deck-access/get-deck-access-by-share-id-db.ts
@@ -9,21 +9,25 @@ const resultSchema = z.object({
   used_by: z.number().nullable(),
 });
 
+type GetDeckAccessByShareIdDbResultType = z.infer<typeof resultSchema>;
+
 export const getDeckAccessByShareIdDb = async (
   envSafe: EnvSafe,
   shareId: string,
-) => {
+): Promise<GetDeckAccessByShareIdDbResultType | null> => {
   const db = getDatabase(envSafe);
 
   const oneTimeShareLinkResult = await db
     .from("deck_access")
     .select("deck_id, author_id, used_by")
     .eq("share_id", shareId)
-    .single();
+    .maybeSingle();
 
   if (oneTimeShareLinkResult.error) {
     throw new DatabaseException(oneTimeShareLinkResult.error);
   }
 
-  return resultSchema.parse(oneTimeShareLinkResult.data);
+  return oneTimeShareLinkResult.data
+    ? resultSchema.parse(oneTimeShareLinkResult.data)
+    : null;
 };
diff --git a/functions/db/deck/get-deck-with-cards-by-id-db.ts b/functions/db/deck/get-deck-with-cards-by-id-db.ts
index 5df99575..958478a1 100644
--- a/functions/db/deck/get-deck-with-cards-by-id-db.ts
+++ b/functions/db/deck/get-deck-with-cards-by-id-db.ts
@@ -1,9 +1,15 @@
 import { DatabaseException } from "../database-exception.ts";
-import { deckWithCardsSchema } from "./decks-with-cards-schema.ts";
+import {
+  DeckWithCardsDbType,
+  deckWithCardsSchema,
+} from "./decks-with-cards-schema.ts";
 import { EnvSafe } from "../../env/env-schema.ts";
 import { getDatabase } from "../get-database.ts";
 
-export const getDeckWithCardsById = async (env: EnvSafe, deckId: number) => {
+export const getDeckWithCardsById = async (
+  env: EnvSafe,
+  deckId: number,
+): Promise<DeckWithCardsDbType> => {
   const db = getDatabase(env);
 
   const stableShareLinkResult = await db
diff --git a/functions/get-shared-deck.test.ts b/functions/get-shared-deck.test.ts
new file mode 100644
index 00000000..36363b80
--- /dev/null
+++ b/functions/get-shared-deck.test.ts
@@ -0,0 +1,139 @@
+import { afterEach, describe, expect, test, vi } from "vitest";
+import { onRequest as getSharedDeckRequest } from "./get-shared-deck.ts";
+import { DeckWithCardsDbType } from "./db/deck/decks-with-cards-schema.ts";
+import { createMockRequest } from "./lib/cloudflare/create-mock-request.ts";
+
+vi.mock("./services/get-user.ts", () => ({
+  getUser: async () => ({ id: 1 }),
+}));
+
+const getDeckAccessByShareIdMock = vi.hoisted(() => vi.fn());
+vi.mock("./db/deck-access/get-deck-access-by-share-id-db.ts", () => ({
+  getDeckAccessByShareIdDb: async () => getDeckAccessByShareIdMock(),
+}));
+
+const createJsonResponseMock = vi.hoisted(() => vi.fn());
+vi.mock("./lib/json-response/create-json-response.ts", () => ({
+  createJsonResponse: async () => createJsonResponseMock(),
+}));
+
+const getDeckWithCardsByIdMock = vi.hoisted(() => vi.fn());
+vi.mock("./db/deck/get-deck-with-cards-by-id-db.ts", () => ({
+  getDeckWithCardsById: async () => getDeckWithCardsByIdMock(),
+}));
+
+const getDeckWithCardsByShareIdDbMock = vi.hoisted(() => vi.fn());
+vi.mock("./db/deck/get-deck-with-cards-by-share-id-db.ts", () => ({
+  getDeckWithCardsByShareIdDb: async () => getDeckWithCardsByShareIdDbMock(),
+}));
+
+const createBadRequestResponseMock = vi.hoisted(() => vi.fn());
+vi.mock("./lib/json-response/create-bad-request-response.ts", () => ({
+  createBadRequestResponse: async () => createBadRequestResponseMock(),
+}));
+
+const startUsingDeckAccessDbMock = vi.hoisted(() => vi.fn());
+vi.mock("./db/deck-access/start-using-deck-access-db.ts", () => ({
+  startUsingDeckAccessDb: async () => startUsingDeckAccessDbMock(),
+}));
+
+const mockDeckOfUser1: DeckWithCardsDbType = {
+  id: 1,
+  name: "name",
+  description: "description",
+  share_id: "share_id",
+  author_id: 1,
+  created_at: new Date().toISOString(),
+  deck_category: null,
+  deck_card: [],
+  is_public: false,
+  speak_field: null,
+  available_in: null,
+  category_id: null,
+  speak_locale: null,
+};
+
+const mockDeckOfUser2: DeckWithCardsDbType = {
+  id: 2,
+  name: "name",
+  description: "description",
+  share_id: "share_id",
+  author_id: 2,
+  created_at: new Date().toISOString(),
+  deck_category: null,
+  deck_card: [],
+  is_public: false,
+  speak_field: null,
+  available_in: null,
+  category_id: null,
+  speak_locale: null,
+};
+
+describe("get shared deck", () => {
+  afterEach(() => {
+    vi.clearAllMocks();
+  });
+
+  test("deck author equals deck", async () => {
+    getDeckAccessByShareIdMock.mockReturnValue({
+      author_id: 1,
+      used_by: null,
+      deck_id: 1,
+    });
+    getDeckWithCardsByIdMock.mockReturnValue(mockDeckOfUser1);
+
+    await getSharedDeckRequest(
+      createMockRequest(`https://example.com?share_id=SHARE_ID1`),
+    );
+
+    expect(getDeckWithCardsByIdMock).toBeCalled();
+    expect(getDeckWithCardsByShareIdDbMock).not.toBeCalled();
+    expect(createBadRequestResponseMock).not.toBeCalled();
+    expect(startUsingDeckAccessDbMock).not.toBeCalled();
+  });
+
+  test("no one time access found", async () => {
+    getDeckAccessByShareIdMock.mockReturnValue(null);
+    getDeckWithCardsByShareIdDbMock.mockReturnValue(mockDeckOfUser1);
+
+    await getSharedDeckRequest(
+      createMockRequest(`https://example.com?share_id=SHARE_ID1`),
+    );
+
+    expect(getDeckWithCardsByIdMock).not.toBeCalled();
+    expect(getDeckWithCardsByShareIdDbMock).toBeCalled();
+    expect(createBadRequestResponseMock).not.toBeCalled();
+    expect(startUsingDeckAccessDbMock).not.toBeCalled();
+  });
+
+  test("one time access found, but already used by another user", async () => {
+    getDeckAccessByShareIdMock.mockReturnValue({
+      author_id: 2,
+      used_by: 2,
+      deck_id: 2,
+    });
+    getDeckWithCardsByIdMock.mockReturnValue(mockDeckOfUser2);
+
+    await getSharedDeckRequest(
+      createMockRequest(`https://example.com?share_id=SHARE_ID1`),
+    );
+
+    expect(createBadRequestResponseMock).toBeCalled();
+  });
+
+  test("one time access found and it is not used", async () => {
+    getDeckAccessByShareIdMock.mockReturnValue({
+      author_id: 2,
+      used_by: null,
+      deck_id: 2,
+    });
+    getDeckWithCardsByIdMock.mockReturnValue(mockDeckOfUser2);
+
+    await getSharedDeckRequest(
+      createMockRequest(`https://example.com?share_id=SHARE_ID1`),
+    );
+
+    expect(getDeckWithCardsByIdMock).toBeCalled();
+    expect(startUsingDeckAccessDbMock).toBeCalled();
+  });
+});
diff --git a/functions/lib/cloudflare/create-mock-request.ts b/functions/lib/cloudflare/create-mock-request.ts
new file mode 100644
index 00000000..ed9b7e55
--- /dev/null
+++ b/functions/lib/cloudflare/create-mock-request.ts
@@ -0,0 +1,13 @@
+export const createMockRequest = (url: string) => {
+  const mockEnv = {
+    BOT_TOKEN: "BOT_TOKEN",
+    SUPABASE_KEY: "SUPABASE_KEY",
+    SUPABASE_URL: "SUPABASE_URL",
+    VITE_BOT_APP_URL: "VITE_BOT_APP_URL",
+  };
+
+  return {
+    request: { url: url },
+    env: mockEnv,
+  } as any;
+};