diff --git a/apps/api/v1/test/lib/selected-calendars/_post.test.ts b/apps/api/v1/test/lib/selected-calendars/_post.test.ts
new file mode 100644
index 0000000000..dea72fdaa5
--- /dev/null
+++ b/apps/api/v1/test/lib/selected-calendars/_post.test.ts
@@ -0,0 +1,121 @@
+import prismaMock from "../../../../../../tests/libs/__mocks__/prismaMock";
+
+import type { Request, Response } from "express";
+import type { NextApiRequest, NextApiResponse } from "next";
+import { createMocks } from "node-mocks-http";
+import { describe, expect, test } from "vitest";
+
+import { HttpError } from "@calcom/lib/http-error";
+
+import handler from "../../../pages/api/selected-calendars/_post";
+
+type CustomNextApiRequest = NextApiRequest & Request;
+type CustomNextApiResponse = NextApiResponse & Response;
+
+describe("POST /api/selected-calendars", () => {
+  describe("Errors", () => {
+    test("Returns 403 if non-admin user tries to set userId in body", async () => {
+      const { req, res } = createMocks<CustomNextApiRequest, CustomNextApiResponse>({
+        method: "POST",
+        body: {
+          integration: "google",
+          externalId: "ext123",
+          userId: 444444,
+        },
+      });
+
+      req.userId = 333333;
+
+      try {
+        await handler(req, res);
+      } catch (e) {
+        expect(e).toBeInstanceOf(HttpError);
+        expect((e as HttpError).statusCode).toBe(403);
+        expect((e as HttpError).message).toBe("ADMIN required for userId");
+      }
+    });
+
+    test("Returns 400 if request body is invalid", async () => {
+      const { req, res } = createMocks<CustomNextApiRequest, CustomNextApiResponse>({
+        method: "POST",
+        body: {
+          integration: "google",
+        },
+      });
+
+      req.userId = 333333;
+      req.isSystemWideAdmin = true;
+
+      await handler(req, res);
+
+      expect(res.statusCode).toBe(400);
+      expect(JSON.parse(res._getData()).message).toBe("invalid_type in 'externalId': Required");
+    });
+  });
+
+  describe("Success", () => {
+    test("Creates selected calendar if user is admin and sets bodyUserId", async () => {
+      const { req, res } = createMocks<CustomNextApiRequest, CustomNextApiResponse>({
+        method: "POST",
+        query: {
+          apiKey: "validApiKey",
+        },
+        body: {
+          integration: "google",
+          externalId: "ext123",
+          userId: 444444,
+        },
+      });
+
+      req.userId = 333333;
+      req.isSystemWideAdmin = true;
+
+      prismaMock.user.findFirstOrThrow.mockResolvedValue({
+        id: 444444,
+      } as any);
+
+      prismaMock.selectedCalendar.create.mockResolvedValue({
+        credentialId: 1,
+        integration: "google",
+        externalId: "ext123",
+        userId: 444444,
+      });
+
+      await handler(req, res);
+
+      expect(res.statusCode).toBe(200);
+      const responseData = JSON.parse(res._getData());
+      expect(responseData.selected_calendar.credentialId).toBe(1);
+      expect(responseData.message).toBe("Selected Calendar created successfully");
+    });
+
+    test("Creates selected calendar if user is non-admin and does not set bodyUserId", async () => {
+      const { req, res } = createMocks<CustomNextApiRequest, CustomNextApiResponse>({
+        method: "POST",
+        query: {
+          apiKey: "validApiKey",
+        },
+        body: {
+          integration: "google",
+          externalId: "ext123",
+        },
+      });
+
+      req.userId = 333333;
+
+      prismaMock.selectedCalendar.create.mockResolvedValue({
+        credentialId: 1,
+        integration: "google",
+        externalId: "ext123",
+        userId: 333333,
+      });
+
+      await handler(req, res);
+
+      expect(res.statusCode).toBe(200);
+      const responseData = JSON.parse(res._getData());
+      expect(responseData.selected_calendar.credentialId).toBe(1);
+      expect(responseData.message).toBe("Selected Calendar created successfully");
+    });
+  });
+});