code: public static void assertLastOperationSuccess(String msg, SipActionObject op) {
      assertNotNull("Null assert object passed in", op);
      assertTrue(msg, op.getErrorMessage().length() == 0);
    }
docs: Asserts that the last SIP operation performed by the given object was successful. Assertion
  failure output includes the given message text.
  
  @param msg message text to output if the assertion fails.
  @param op the SipUnit object that executed an operation.