If you have code that is part of your app, and you can move it into a gem, then you do not need to run the tests on that gem every time, but only when that gem changes. (For example, we don't run the Rails test suite every time we make an application change)
Noel: "Do we need to start pulling functionality out of this app and rewriting this piece by piece in services? Which is effectively what that place wound up doing. They wound up slowly killing off their monolithic Rails application by putting pieces of it into smaller services that interacted. And writing those services hopefully, although I don't know for sure, hopefully those services will be written with faster test suites of their own and then also solve the problem of having to run the whole test suite for every change. But that is a long process that has a long-term benefit and not a short-term benefit. And I think different environments are going to be differently receptive to that."