Add ability to use LIBBPF_DEBUG=1 for BPF tests

[gmarler]

• This allows getting BPF verifier debug output when such tests fail

[javierhonduco]

This is false by default as it's a reasonable setting to have unless something it's set on purpose.

I recommend to either manually add it for each test such as it's done in

lightswitch/tests/integration_test.rs

Line 323 in 60048b3

let bpf_test_debug = std::env::var("TEST_DEBUG_BPF").is_ok();

, or that a a constructor for testing purposes is created

[gmarler]

Sure, can do that - but this keeps the value false by default (and has the benefit of only having to be set in one place with one change - which I thought was a virtue) - one has to set LIBBPF_DEBUG to get a value other than false.

Relatedly, did you want me to change LIBBPF_DEBUG to TEST_DEBUG_BPF, for consistency across the codebase? Or was the intent different?

[javierhonduco]

I think it's too "magical" to use env vars for things like this, that's why I prefer hardcoding it / selecting it at runtime. The reason for this is that typically env vars are not very well documented.

I think TEST_LIBBPF_DEBUG makes more sense, definitely would be good to have a single env var name for this purpose. But as long as we are consistent on using one name I don't mind too much which one we choose!