I would like to test my application that connects to a third party system via JMS on an IBM MQ broker (Fircosoft) in isolation, and be able to simulate error responses and set up test data. How can I simulate a third party JMS IBM MQ API, are there any special tools I can use?
You can use an IBM MQ mocking/simulation/service virtualization tool, for example Traffic Parrot. Have a look at this mocking and simulating JMS IBM® WebSphere MQ tutorial, it will take you step by step how to do it.