Needs environment variable
Skip code (such as a test) at compile time if an environment variable is undefined.
Example
some_test
will not be compiled if SOMEENVIRONMENTVARIABLE
is not defined:
use *;
// or if its specified value not matched
Note: As needs_env_var
is evaluated at compile time you need to force a re-compilation an environment variable
is defined after compilation, e.g. with cargo clean
.