message: Add: purser-core `messageOrDataValidator` mock function
diff: @@ -19,3 +19,12 @@ export const verifyMessageSignature = jest.fn();
  export const recoverPublicKey = jest.fn(() => 'recovered-mocked-public-key');
  export const userInputValidator = jest.fn();
  +
  +export const messageOrDataValidator = jest.fn(
  + ({ message, messageData } = {}) => {
  + if (message) {
  + return message;
  + }
  + return messageData;
  + },
  +);
  