test(frontend): mockIdentity transformRequest (#3355)

# Motivation

Spotted this check in NNS dapp which prevents the `mockIdentity` to be
used without knowing. Thought it can be interesting for future proof to
have it in OISY as well.

src/frontend/src/tests/mocks/identity.mock.ts

@@ -5,8 +5,17 @@ export const mockPrincipalText = 'xlmdg-vkosz-ceopx-7wtgu-g3xmd-koiyc-awqaq-7mod
 
 export const mockPrincipal = Principal.fromText(mockPrincipalText);
 
+const transformRequest = () => {
+	console.error(
+		'It looks like the agent is trying to make a request that should have been mocked at',
+		new Error().stack
+	);
+	throw new Error('Not implemented');
+};
+
 export const mockIdentity = {
-	getPrincipal: () => mockPrincipal
+	getPrincipal: () => mockPrincipal,
+	transformRequest
 } as unknown as Identity;
 
 // This is not linked/related to the mock above.