add unit tests and minor fixes for resolveCollectorRefs()

[hhromic]

After my shameful programming errors in PR #194, some of them reported in #210 and fixed in #208, I decided to shield the codebase a bit against this type of mistakes by adding unit tests for the resolveCollectorRefs() function. In particular:

• NoGlobbing test: checks that non-globbed collector references are correctly resolved.
• Globbing test: checks that globbed collector references are correctly resolved.
• NoCollectorRefs test: checks that resolveCollectorRefs() resolves to empty when no collector references are given.
• UnknownCollector test: checks that resolveCollectorRefs() errors correctly when a collector reference is invalid.

All of the above tests (with the exception of Globbing) pass with the implementation in 0.9.3 (before globbing support).

Only the NoCollectorRefs test passes with the implementation in 0.10.0 (after globbing support => apologies again!).

The NoCollectorRefs and UnknownCollector tests do not pass with the implementation in master (after the fix in #208). The NoGlobbing test passes/fails in a non-deterministic manner because resolveCollectorRefs() no longer returns the resolved collectors in the same order as in 0.9.3. Note that order does not really matter, but still wanted to stay correct.

All of the above is now also fixed in a second commit in this PR, bringing resolveCollectorRefs() to its previous behaviour when not using globbing patterns in collector references:

• return non-globbed resolved collectors in the order they are found
• do not error when no collectors are resolved

The Makefile and the GitHub build.yml workflow in the project already have testing support, so all of this will be automatically executed in future PRs/commits. For example:

Local machine:

$ make test
>> running tests
?       github.com/burningalchemist/sql_exporter        [no test files]
?       github.com/burningalchemist/sql_exporter/cmd/sql_exporter       [no test files]
?       github.com/burningalchemist/sql_exporter/errors [no test files]
ok      github.com/burningalchemist/sql_exporter/config 0.036s

GitHub workflow:

I hope this helps to avoid these silly mistakes in future contributions :)

--

fixes #210

[burningalchemist]

Hey @hhromic, thanks heaps for the fix and introducing tests - this is a memorable event! 🚀

I plan to refactor the code, but before that a good test coverage is a must. So you definitely improved my motivation. 😃

Thanks again and no worries about the issue. 🙂👍

[hhromic]

I plan to refactor the code, but before that a good test coverage is a must. So you definitely improved my motivation. 😃

I fully understand what it is to be unmotivated, so I'm glad you feel more motivated!
As I mentioned in the test suite source, I think a nice improvement for the codebase is to implement typed errors consistently. Recent versions of Go have very nice support for wrapped errors too. Maybe I can find some time to help you with that if you want to go into this direction.

Thanks again and no worries about the issue. 🙂👍

Happy to help. I still have pending to implement configuration via env variables :) :)