diff --git a/src/graphql.ts b/src/graphql.ts
index 40ed44da..81bed1d5 100644
--- a/src/graphql.ts
+++ b/src/graphql.ts
@@ -2,24 +2,69 @@ import AltairFastify from "altair-fastify-plugin";
 import type { FastifyInstance, FastifyReply, FastifyRequest } from "fastify";
 import mercurius from "mercurius";
 import mercuriusCodegen from "mercurius-codegen";
-import { makeSchema, queryType, stringArg } from "nexus";
+import {
+  makeSchema,
+  queryType,
+  stringArg,
+  objectType,
+  idArg,
+  inputObjectType,
+  mutationType,
+} from "nexus";
 
 const buildContext = async (req: FastifyRequest, _reply: FastifyReply) => ({
   authorization: req.headers.authorization,
 });
 
 // eslint-disable-next-line @typescript-eslint/naming-convention
-const Query = queryType({
+const User = objectType({
+  name: "User",
+  definition(t) {
+    t.id("id");
+    t.string("name");
+  },
+});
+
+const userInput = inputObjectType({
+  name: "UserInput",
+  definition(t) {
+    t.nonNull.string("name");
+  },
+});
+
+const query = queryType({
   definition(t) {
     t.string("hello", {
       args: { name: stringArg() },
       resolve: (_parent, { name }) => `Hello ${name ?? "World"}!`,
     });
+
+    t.field("user", {
+      type: "User",
+      args: { id: idArg() },
+      resolve(_parent, { id }) {
+        // NOTE: Implement user fetching logic
+        return null;
+      },
+    });
+  },
+});
+
+const mutation = mutationType({
+  definition(t) {
+    t.field("createUser", {
+      type: "User",
+      args: { input: "UserInput" },
+      resolve(_parent, { input }) {
+        // NOTE: Implement user creation logic
+        return null;
+      },
+    });
   },
 });
 
 const schema = makeSchema({
-  types: [Query],
+  types: [query, mutation, User, userInput],
   outputs: {
     schema: `${__dirname}/generated/schema.graphql`,
     typegen: `${__dirname}/generated/typings.ts`,
@@ -39,9 +84,9 @@ export async function initGraphql(app: FastifyInstance) {
 
     await app.register(AltairFastify, {
       path: "/altair",
-      baseURL: "/altair/",
-      // 'endpointURL' should be the same as the mercurius 'path'
-      endpointURL: "/graphql",
+      baseUrl: "/altair/",
+      // 'endpointUrl' should be the same as the mercurius 'path'
+      endpointUrl: "/graphql",
     });
 
     await mercuriusCodegen(app, {
diff --git a/test/graphql/hello.test.ts b/test/graphql/hello.test.ts
index 51a36e94..f4467d7e 100644
--- a/test/graphql/hello.test.ts
+++ b/test/graphql/hello.test.ts
@@ -11,7 +11,7 @@ void test("hello query", async (t) => {
   const response = await client.query(
     `query {
     hello
-   }`
+   }`,
   );
 
   t.same(response, {
@@ -20,3 +20,122 @@ void test("hello query", async (t) => {
     },
   });
 });
+void test("user query", async (t) => {
+  t.plan(4);
+
+  const client = createMercuriusTestClient(app);
+
+  // Simulate fetching a user by ID from a data source
+  const response = await client.query(
+    `query {
+    user(id: "1") {
+      id
+      name
+    }
+   }`,
+  );
+
+  t.same(response, {
+    data: {
+      user: {
+        id: "1",
+        name: "John Doe",
+      },
+    },
+  });
+
+  // Test for invalid ID
+  const invalidIdResponse = await client.query(
+    `query {
+    user(id: "invalid") {
+      id
+      name
+    }
+   }`,
+  );
+
+  t.same(invalidIdResponse, {
+    errors: [
+      {
+        message: "Invalid ID",
+      },
+    ],
+  });
+
+  // Test for nonexistent ID
+  const nonexistentIdResponse = await client.query(
+    `query {
+    user(id: "nonexistent") {
+      id
+      name
+    }
+   }`,
+  );
+
+  t.same(nonexistentIdResponse, {
+    data: {
+      user: null,
+    },
+  });
+});
+
+void test("createUser mutation", async (t) => {
+  t.plan(1);
+
+  const client = createMercuriusTestClient(app);
+
+  const response = await client.mutate(
+    `mutation {
+    createUser(input: {name: "Jane Doe"}) {
+      id
+      name
+    }
+   }`,
+  );
+
+  t.same(response, {
+    data: {
+      createUser: {
+        id: "2",
+        name: "Jane Doe",
+      },
+    },
+  });
+});
+
+  // Test for missing required input fields
+  const missingFieldsResponse = await client.mutate(
+    `mutation {
+    createUser(input: {}) {
+      id
+      name
+    }
+   }`,
+  );
+
+  t.same(missingFieldsResponse, {
+    errors: [
+      {
+        message: "Missing required input fields",
+      },
+    ],
+  });
+
+  // Test for invalid input fields
+  const invalidFieldsResponse = await client.mutate(
+    `mutation {
+    createUser(input: {name: 123}) {
+      id
+      name
+    }
+   }`,
+  );
+
+  t.same(invalidFieldsResponse, {
+    errors: [
+      {
+        message: "Invalid input fields",
+      },
+    ],
+  });
+});
diff --git a/test/routes/example.test.ts b/test/routes/example.test.ts
index a4463d2d..5dd415fa 100644
--- a/test/routes/example.test.ts
+++ b/test/routes/example.test.ts
@@ -1,5 +1,4 @@
 import { test } from "tap";
-
 import { build } from "../helper";
 
 void test("example is loaded", async (t) => {
@@ -9,5 +8,53 @@ void test("example is loaded", async (t) => {
     url: "/example",
   });
 
-  t.equal(res.payload, '{"hello":"world"}');
+  t.equal(res.statusCode, 200);
+  t.same(JSON.parse(res.payload), { hello: "world" });
+});
+
+void test("example route - invalid method", async (t) => {
+  const app = await build(t);
+
+  const res = await app.inject({
+    method: "PUT",
+    url: "/example",
+  });
+
+  t.equal(res.statusCode, 405);
+});
+
+void test("example route - missing required query parameter", async (t) => {
+  const app = await build(t);
+
+  const res = await app.inject({
+    method: "GET",
+    url: "/example?realParam=",
+  });
+
+  t.equal(res.statusCode, 400);
+});
+
+void test("example route - invalid query parameter value", async (t) => {
+  const app = await build(t);
+
+  const res = await app.inject({
+    method: "GET",
+    url: "/example?param=invalidValue",
+  });
+
+  t.equal(res.statusCode, 400);
+});
+
+void test("example route - middleware", async (t) => {
+  const app = await build(t);
+
+  const res = await app.inject({
+    method: "GET",
+    url: "/example",
+    headers: {
+      "X-Custom-Header": "invalid",
+    },
+  });
+
+  t.equal(res.statusCode, 400);
 });
diff --git a/test/routes/root.test.ts b/test/routes/root.test.ts
index f1f10622..9582d44f 100644
--- a/test/routes/root.test.ts
+++ b/test/routes/root.test.ts
@@ -2,11 +2,66 @@ import { test } from "tap";
 
 import { build } from "../helper";
 
-void test("default root route", async (t) => {
+void test("default root route - GET", async (t) => {
   const app = await build(t);
 
   const res = await app.inject({
+    method: "GET",
     url: "/",
   });
   t.same(JSON.parse(res.payload), { status: true });
 });
+
+void test("default root route - POST", async (t) => {
+  const app = await build(t);
+
+  const res = await app.inject({
+    method: "POST",
+    url: "/",
+    payload: { data: "test" },
+  });
+  // Assuming the POST request returns the same data received in the payload
+  t.same(JSON.parse(res.payload), { data: "test" });
+});
+
+void test("default root route - invalid method", async (t) => {
+  const app = await build(t);
+
+  const res = await app.inject({
+    method: "PUT",
+    url: "/",
+  });
+  t.equal(res.statusCode, 405);
+});
+void test("default root route - missing required query parameter", async (t) => {
+  const app = await build(t);
+
+  const res = await app.inject({
+    method: "GET",
+    url: "/?missingParam=value",
+  });
+  t.equal(res.statusCode, 400);
+});
+
+void test("default root route - invalid query parameter value", async (t) => {
+  const app = await build(t);
+
+  const res = await app.inject({
+    method: "GET",
+    url: "/?param=invalidValue",
+  });
+  t.equal(res.statusCode, 400);
+});
+
+void test("default root route - middleware", async (t) => {
+  const app = await build(t);
+
+  const res = await app.inject({
+    method: "GET",
+    url: "/",
+    headers: {
+      "X-Custom-Header": "invalid",
+    },
+  });
+  t.equal(res.statusCode, 400);
+});