Shifts the testing of buildpack env vars handling slightly more towards integration tests rather than unit tests, since a big part of env var handling is ensuring the env is passed around correctly + aspects like the automatic env vars added by libcnb and lifecycle, which can only be properly tested via integration tests.
Adds more testing of broken user-provided env vars, by passing them in by default for all tests (instead of a single test), and by adding more broken env vars to the list.
In the unit tests, switches the example layer location to one that's more obviously an example path, to prevent anyone reading the tests from thinking that's the actual location set by the buildpack.
This change will help validate the env var handling remains consistent with the upcoming transition to libcnb.rs' struct layer API.
This change will help validate the env var handling remains consistent with the upcoming transition to libcnb.rs' struct layer API.
GUS-W-16261336.