Your specific task sounds like maybe it calls for Wiremock, since it is presumably a third party HTTP API and you'd like to pretend this service has some defined behaviour while testing your integration does what you expect.
I found wiremock to be excellent. What I really struggled with was mocking out other bits of rust code or setting up the DB with the right data and wiping it after the test. All this stuff that just comes for free in other language/test setups you have to manually reimplement.
