The issue was rather about the fact that changing that single .py file can have impact on a service A and service B which depend on service C where the file was

The issue was rather about the fact that changing that single .py file can have impact on a service A and service B which depend on service C where the file was changed. In microservice world, you have to run e2e tests because thats the only place where you can really guarantee the system will work as you expect. Pacts wont solve that, integration test - the same, units w/e. Running a monolith test is overall faster than spinning 20 microservices, beinging every db to specific atate and running tests.