agave-validator: add args tests for set-log-filter

[yihau]

Problem

#4082

Summary of Changes

extracting args parsing logic and adding tests

[yihau]

we used let filter = value_t_or_exit!(matches, "filter", String); which exits if filter isn't present. it makes the test become tricky. I change it to matches.value_of("filter").map(|s| s.to_string()) and moved the exit logic to the fn execute as a workaround. this shouldn't affect the original use case and also allows us to add tests to ensure the process works correctly. my plan is to build all tests first, giving us more confidence to proceed with deeper refactoring or upgrading to clap v3/v4 directly.

[steviez]

we used let filter = value_t_or_exit!(matches, "filter", String); which exits if filter isn't present. it makes the test become tricky. I change it to matches.value_of("filter").map(|s| s.to_string()) and moved the exit logic to the fn execute as a workaround. this shouldn't affect the original use case and also allows us to add tests to ensure the process works correctly. my plan is to build all tests first, giving us more confidence to proceed with deeper refactoring or upgrading to clap v3/v4 directly.

I'm not sure I like this change. Namely, I don't think we should be making the "production" case more convoluted for the "test" case.

As an alternative, I think we could use value_t!() instead of value_t_or_exit!(). This means the parse function can now return a Result, and then we can handle the result above.

I think this format will absolutely be necessary when it comes time to port the run command over

[yihau]

it's ready for another review! for now it's using value_t and map err.