diff --git a/packages/protobuf-demo/src/demo.spec.ts b/packages/protobuf-demo/src/demo.spec.ts
index d1da48ef..7a03412b 100644
--- a/packages/protobuf-demo/src/demo.spec.ts
+++ b/packages/protobuf-demo/src/demo.spec.ts
@@ -1,5 +1,47 @@
-describe("demo", () => {
-  it("runs", () => {
-    expect(true).toEqual(false);
+import { assert } from "@cosmjs/utils";
+
+import { cosmos_sdk as cosmosSdk, google } from "./generated/codecimpl";
+
+const { Coin } = cosmosSdk.v1;
+const { TxBody } = cosmosSdk.tx.v1;
+const { MsgSend } = cosmosSdk.x.bank.v1;
+const { Any } = google.protobuf;
+
+describe("protobuf demo", () => {
+  it("works", () => {
+    const coin = Coin.create({
+      denom: "ucosm",
+      amount: "1234567890",
+    });
+    const msgSend = MsgSend.create({
+      fromAddress: Uint8Array.from(Array.from({ length: 20 }, () => 1)),
+      toAddress: Uint8Array.from(Array.from({ length: 20 }, () => 2)),
+      amount: [coin],
+    });
+
+    // Serialization
+    const msgSendBytes = MsgSend.encode(msgSend).finish();
+    const msgSendWrapped = Any.create({
+      // eslint-disable-next-line @typescript-eslint/camelcase
+      type_url: "xxx",
+      value: msgSendBytes,
+    });
+    const txBody = TxBody.create({
+      messages: [msgSendWrapped],
+      memo: "Some memo",
+      timeoutHeight: 9999,
+      extensionOptions: [],
+    });
+    const txBodyBytes = TxBody.encode(txBody).finish();
+
+    // Deserialization
+    const txBodyDecoded = TxBody.decode(txBodyBytes);
+    assert(txBodyDecoded.messages[0].value);
+    const msgSendDecoded = MsgSend.decode(txBodyDecoded.messages[0].value);
+
+    // fromAddress and toAddress are now Buffers
+    expect(Uint8Array.from(msgSendDecoded.fromAddress)).toEqual(msgSend.fromAddress);
+    expect(Uint8Array.from(msgSendDecoded.toAddress)).toEqual(msgSend.toAddress);
+    expect(msgSendDecoded.amount).toEqual(msgSend.amount);
   });
 });