In almost all the Maximo projects, we do have interfaces created to external systems by different protocols, we test them on regular basis after each fix or releases to ensure there is no failure on the integration.
SOAPUI is open source tool that is used to test WebService or WebAPI Testing. It can test protocols such as SOAP over http/jms, REST.
We can extend this tool to automate the Maximo Integrations.
It offers components to send/receive messages, delays, transfer properties and groovy script [similar to python] knowledge is needed to get started.
A sample project for testing OOB Maximo scenario.
https://github.com/bysurendar/maximo_testing/tree/master/SOAPUI_MIF_Testing
References:
SOAPUI tutorials - https://www.soapui.org/getting-started/your-first-soapui-project.html