Is there a way to un-set environment variables? I have one set in my pants.toml that I need to unset in a CI configuration.

extra_env_vars

can set more variables, but I can't seem to find a way to un-set them.

Does it have to “not exist”, rather than being just empty?

--test-extra-env-vars

is a list option so the remove notation described at https://www.pantsbuild.org/docs/options#addremove-semantics should allow you to delete the variable from extra_env_vars

yeah it has to not exist

and if you have a CI-specific config file, you can also just set the exact set of env vars you need for CI (vs using the remove notation)