chore: use testify instead of t.Fatal

[mmorel-35]

This uses testify instead of testing for t.Fatal calls

[mmorel-35]

/cc @SuperQ

[bwplotka]

Thanks for this, but the last maintainer's decision is to not include extra dependencies which are not mandatory for the project. While a bit verbose, we kept client_golang without testify for long and it would be nice to keep that.

[bwplotka]

We don't want to add extra dependency on purpose in client_golang for little value.

[mmorel-35]

Alright, let's close this one

[beorn7]

In this case, it's not so much about the added dependency, but about the controversial nature of testing frameworks within the Go community. There is a school of Go that recommends to only use the standard library tools for testing. prometheus/client_golang is so widely used that we would rather stick to the common ground here.

Personally, I think a testing framework is fine within a certain group of developers that have found a consensus to use it. That's the reason why testify is used in prometheus/prometheus. However, prometheus/client_golang is used by ~everyone, which is again a reason to keep the code as "normal" as possible so everyone can read it without learning a special framework first.