Automated system-level testing

Hello r/softwaredevelopment

Was wondering what are some tools/processes that will allow us to do automated system-level testing? I say system-level, because we inherited a monolithic Java backend application that interfaces with a DB and a message broker. Of course, there are no existing tests, but we need to develop tests that hopefully can fit in a CI pipeline in the future.

So my main question is: is there a test tool where we can automatically test the entire Java application against the other external entities (DB & message broker)?