The virtualenv path in the xshell-type builder appears not to activate properly on Windows, giving the following type of problem:

[75011716] $ cmd.exe /c call C:\Users\jenkins\AppData\Local\Temp\shiningpanda7607611870788630234.bat

C:\Jenkins\workspace\testfixtures-virtualenv\75011716>pip install -e .[test,build]
'pip' is not recognized as an internal or external command,
operable program or batch file.