When developing software that exchanges data with other components or services you may be confronted with the proper simulation of those foreign services during integration testing. This is because you need to connect with a foreign service
that is simply not available on your local machine or in a test environment.

For unit testing purpose you can use mocks that help out to simulate proper responses. There will be times where your software is deployed to a test environment
in order to perform some acceptance tests with your stakeholders before going to a final release. Usually this is also done with the customer exploring the software through manual testing. In these situations traditional service mocking is not
a good option and you need a real simulator instance that receives requests and responds with proper test data.

This is exactly what the Citrus simulator project provides for you. Standalone simulation and complex request/response processing with solid validation capabilities. The Citrus simulator provides a very easy and reliable definition of inbound and outbound messages for different scenarios.
Good news is that this is not only for Http REST interfaces but also for SOAP WebService, JMS, RMI, mail messaging and many more. So you can use the simulator whenever you need to integrate with another service that is simply not available on your local machine or in your test environment.

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