statler:[~/src/pants][master]$ ./v2 test src/python/pants/source/source_root_test.py 
05:05:20 [INFO] initializing pantsd...
05:05:21 [INFO] pantsd initialized.
22:05:23.21 [INFO] Wrote dist/pants_local_binary.pex
Finished bootstrapping pants.pex for integration tests.

22:05:24.97 [ERROR] panic at 'called `Result::unwrap()` on an `Err` value: "Field `env` was not convertible to type alloc::vec::Vec<alloc::string::String>: PyErr { ptype: <class \'TypeError\'>, pvalue: Some(\'Expected type that converts to PyString but received tuple\'), ptraceback: None }"', src/externs/mod.rs:195
22:05:24.97 [ERROR] Please set RUST_BACKTRACE=1, re-run, and then file a bug at <https://github.com/pantsbuild/pants/issues>.