Hi! This question is about best practices for testing applications that use client_golang to instrument with custom metrics and avoiding the dreaded "duplicate metrics collector registration attempted".
Let's say I have an HTTP handler for an app that keeps a counter. The counter can be page hits, orders submitted, whatever. Let's say my handler, a struct with ServeHTTP attached, refers to this counter either as a package level variable or as a a struct member. I've seen the same behavior either way. Suppose I keep the typical patterns: use promauto, register my Collectors in New, or register my collectors at package initialization. When I put my handler under test, I typically create a handler per test. This causes me to bump into "duplicate metrics collector registration attempted". Some ways I have worked around this are to create a single httptest.Server with my handler in TestMain, or attach a RegisterMetrics to defer collector registration where I'm wiring up my dependencies (often main's main func) and just not register the metrics under test. The former makes it harder to inject mocks with different behaviors, the latter makes it hard to test my metrics. So, the questions are: 1) What are some good ways to deal with metric registration under test? 2) Is testing metrics a typical practice, or do you just trust them? In the contrived example, it may be reasonably safe to just trust it, but I'm confident we have seen those cases where there is some tricky behavior around our metrics and we want to be sure we have it right. 3) When testing metrics, such as in an exporter concept where that is in fact the key behavior, is it typical to test the metrics endpoint with an http call (say, with httptest.Server) or do you look at the values held by the collectors? Thanks! Victor -- You received this message because you are subscribed to the Google Groups "Prometheus Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to prometheus-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/prometheus-users/3632f922-7287-4516-8d53-5587e8af6ef1%40googlegroups.com.
