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by john-shaffer
1585 days ago
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In production, I may only want one connection pool to a DB, and in that case global state is pretty much equivalent to passing state as an argument. Development in a Clojure REPL is a different story. I have one connection pool for the dev server, and a separate pool to run tests against. The test db is re-created from a template between each test run, without affecting the dev db at all. I can trivially have multiple test pools if I want to run tests concurrently. I also have a separate service that the server makes calls to, which doesn't run on this server in production (it has its own production server), but does run in dev and test. Each dev/test system runs a separate instance of this service, which has its own separate connection pool(s), and setting this up was trivial. Needless to say, failures are reproducible and meaningful. There is no mocking -- we test against real local services with real local DBs. (There are still some remote service calls which I'm slowly replacing, and some flakey, unavoidable remote dependencies in a few browser tests). I didn't do anything special to make this possible other than naming the config files "service-name-config" instead of just "config". It is just the natural result of passing state in explicit arguments. The same is not true of global state. |
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> It is just the natural result of passing state as explicit arguments.
But nothing you've mentioned here is intrinsic to mutable state. It seems like all that's happened is you identified a part of your program that you wanted to be configurable and exposed a configuration knob. If for example you wanted to make it so that there is a test mode that where you want to prefix "test-" to every string written to the DB that would also probably involve a new argument somewhere. There's nothing here special about the mutable state part of it.