Summary: if you concatenate filenames into /STDOUT and /STDERR in a $zf(-100) call, quote them.
I hit an <ILLEGAL VALUE> error from the following that initially stumped me. This was part of a unit test that worked perfectly fine on Windows, but when CI ran on Docker it failed:
Set outFile = ##class(%Library.File).TempFilename()
Set outDir = ##class(%Library.File).NormalizeDirectory(##class(%Library.File).TempFilename()_"dir-out")
Do##class(%Library.File).CreateDirectoryChain(outDir)
Do$$$AssertEquals($zf(-100,"/STDOUT="_outFile_"/STDERR="_outFile,"tar","-xvf",tempDir_".tgz","-C",outDir).png)
.png)

