diff --git a/dev_deps.ts b/dev_deps.ts
index 3a00c34..8f97861 100644
--- a/dev_deps.ts
+++ b/dev_deps.ts
@@ -1,2 +1 @@
 export { assertEquals } from "https://deno.land/std@0.196.0/assert/mod.ts";
-export * as mf from "https://deno.land/x/mock_fetch@0.3.0/mod.ts";
diff --git a/tests/subscription.test.ts b/tests/subscription.test.ts
index 4f8a586..110e739 100644
--- a/tests/subscription.test.ts
+++ b/tests/subscription.test.ts
@@ -13,8 +13,11 @@ const subscriptionInput = {
     "external_id": "54321",
     "billing_time": "calendar",
     "subscription_at": "2022-08-08T00:00:00Z",
+    "purchase_order_number": "PO-123",
   },
-} satisfies SubscriptionCreateInput;
+} satisfies SubscriptionCreateInput & {
+  subscription: { purchase_order_number: string };
+};
 
 const subscriptionResponse = {
   "subscription": {
@@ -34,8 +37,11 @@ const subscriptionResponse = {
     "previous_plan_code": "previous_code",
     "next_plan_code": "next_code",
     "downgrade_plan_date": "2022-09-14T16:35:31Z",
+    "purchase_order_number": "PO-123",
   },
-} satisfies Subscription;
+} satisfies Subscription & {
+  subscription: { purchase_order_number: string };
+};
 
 const subscriptionsResponse = {
   subscriptions: [subscriptionResponse.subscription],
@@ -50,6 +56,7 @@ Deno.test("Successfully sent subscription responds with 2xx", async (t) => {
     inputParams: [subscriptionInput],
     responseObject: subscriptionResponse,
     status: 200,
+    expectedBody: subscriptionInput,
   });
 });
 
@@ -76,6 +83,7 @@ Deno.test(
       inputParams: ["id", subscriptionInput],
       responseObject: subscriptionResponse,
       status: 200,
+      expectedBody: subscriptionInput,
     });
   },
 );
diff --git a/tests/utils.ts b/tests/utils.ts
index f006108..a641542 100644
--- a/tests/utils.ts
+++ b/tests/utils.ts
@@ -1,6 +1,5 @@
 // deno-lint-ignore-file no-explicit-any ban-types
 import { assertEquals } from "../dev_deps.ts";
-import { mf } from "../dev_deps.ts";
 import { Client, getLagoError } from "../mod.ts";
 import type {
   Api,
@@ -27,10 +26,20 @@ type ExtractLagoResponse<E> = E extends (
 
 const errorMessage = "Lago Error" as const;
 
-export function setupMockClient(route: string, handler: mf.MatchHandler) {
-  const { fetch, mock } = mf.sandbox();
+type MatchHandler = (request: Request) => Response | Promise<Response>;
 
-  mock(route, handler);
+export function setupMockClient(route: string, handler: MatchHandler) {
+  const [method, path] = route.split("@");
+
+  const fetch = (async (input: RequestInfo | URL, init?: RequestInit) => {
+    const request = input instanceof Request ? input : new Request(input, init);
+    const url = new URL(request.url);
+
+    assertEquals(request.method, method);
+    assertEquals(url.pathname, path);
+
+    return await handler(request);
+  }) as typeof globalThis.fetch;
 
   return Client("api_key", { customFetch: fetch });
 }
@@ -48,6 +57,7 @@ export async function lagoTest<
     status,
     testType,
     urlParams,
+    expectedBody,
   }: {
     testType: "error" | "200";
     t: Deno.TestContext;
@@ -59,17 +69,21 @@ export async function lagoTest<
     >;
     status: number;
     urlParams?: Record<string, string>;
+    expectedBody?: unknown;
   },
 ) {
   const client = setupMockClient(
     route,
-    (_req) => {
+    async (_req) => {
       if (urlParams) {
         const urlSearchParams = new URLSearchParams(new URL(_req.url).search);
         Object.entries(urlParams).forEach(([key, value]) => {
           assertEquals(urlSearchParams.get(key), value);
         });
       }
+      if (expectedBody) {
+        assertEquals(await _req.json(), expectedBody);
+      }
       return new Response(
         responseObject ? JSON.stringify(responseObject) : null,
         { status },
diff --git a/tests/wallet.test.ts b/tests/wallet.test.ts
index 4e0b86d..395066c 100644
--- a/tests/wallet.test.ts
+++ b/tests/wallet.test.ts
@@ -15,8 +15,24 @@ const walletInput = {
     "granted_credits": 10,
     "external_customer_id": "12345",
     "expiration_at": "2022-09-14T23:59:59Z",
+    "purchase_order_number": "PO-123",
+    "recurring_transaction_rules": [
+      {
+        "trigger": "interval",
+        "interval": "monthly",
+        "method": "fixed",
+        "paid_credits": 100,
+        "granted_credits": 10,
+        "purchase_order_number": "PO-RULE-123",
+      },
+    ],
   },
-} as const satisfies WalletInput;
+} satisfies WalletInput & {
+  wallet: {
+    purchase_order_number: string;
+    recurring_transaction_rules: Array<{ purchase_order_number: string }>;
+  };
+};
 
 const walletResponse = {
   "wallet": {
@@ -35,15 +51,35 @@ const walletResponse = {
     "last_balance_sync_at": "2022-09-14T16:35:31Z",
     "last_consumed_credit_at": "2022-09-14T16:35:31Z",
     "terminated_at": "2022-09-14T16:35:31Z",
+    "purchase_order_number": "PO-123",
+    "recurring_transaction_rules": [
+      {
+        "lago_id": "483da83c-c007-4fbb-afcd-b00c07c41ffe",
+        "trigger": "interval",
+        "interval": "monthly",
+        "method": "fixed",
+        "paid_credits": 100,
+        "granted_credits": 10,
+        "purchase_order_number": "PO-RULE-123",
+      },
+    ],
   },
-} as const satisfies Wallet;
+} satisfies Wallet & {
+  wallet: {
+    purchase_order_number: string;
+    recurring_transaction_rules: Array<{ purchase_order_number: string }>;
+  };
+};
 
 const walletUpdateInput = {
   "wallet": {
     "name": "Wallet name",
     "expiration_at": "2022-09-14T23:59:59Z",
+    "purchase_order_number": "PO-123",
   },
-} as const satisfies WalletUpdateInput;
+} satisfies WalletUpdateInput & {
+  wallet: { purchase_order_number: string };
+};
 
 const walletsResponse = {
   wallets: [walletInput.wallet],
@@ -58,6 +94,7 @@ Deno.test("Successfully sent wallet responds with 2xx", async (t) => {
     inputParams: [walletInput],
     responseObject: walletResponse,
     status: 200,
+    expectedBody: walletInput,
   });
 });
 
@@ -82,6 +119,7 @@ Deno.test("Successfully sent wallet update request responds with 2xx", async (t)
     inputParams: ["id", walletUpdateInput],
     responseObject: walletResponse,
     status: 200,
+    expectedBody: walletUpdateInput,
   });
 });
 
diff --git a/tests/wallet_transaction.test.ts b/tests/wallet_transaction.test.ts
index b73c4f0..0911568 100644
--- a/tests/wallet_transaction.test.ts
+++ b/tests/wallet_transaction.test.ts
@@ -6,8 +6,11 @@ const walletTransactionInput = {
     "wallet_id": "985da83c-c007-4fbb-afcd-b00c07c41ffe",
     "paid_credits": 100,
     "granted_credits": 10,
+    "purchase_order_number": "PO-123",
   },
-} as const satisfies WalletTransactionInput;
+} satisfies WalletTransactionInput & {
+  wallet_transaction: { purchase_order_number: string };
+};
 
 Deno.test(
   "Successfully sent wallet transaction responds with 2xx",
@@ -27,12 +30,14 @@ Deno.test(
             transaction_type: "inbound",
             amount: 500,
             credit_amount: 500,
+            purchase_order_number: "PO-123",
             settled_at: "2022-09-14T16:35:31Z",
             created_at: "2022-09-14T16:35:31Z",
           },
         ],
       },
       status: 200,
+      expectedBody: walletTransactionInput,
     });
   },
 );