Some RunCMake tests unset some environment variables that affect ctest's
behavior before running it. Any test using the RunCTest helper needs to
do this, so do it in the helper itself.
Issue: #24153
When processing the reset operation in the context of a CTest
`ENVIRONMENT_MODIFICATION` property, the value the variable is reset to
is the one it had after `ENVIRONMENT` was processed, not before.
This was broken once during refactoring and is subtle enough that it
should be tested.
This property allows projects to modify environment variables at test
time rather than trying to guess what the state should be based on what
is present at configure time. Of particular interest is the ability to
use a `PATH` present at test time while adding entries known to be
necessary for the test itself.
There are multiple operations provided to modify variables, including:
- setting and unsetting
- appending and prepending as:
- strings
- path lists
- CMake lists
Additionally, a `reset` action is provided to cancel any prior
modifications to that particular variable in the case of incremental
additions to the test property.
Brad King