This PR just tidies up some tests by removing unused code:
1. If the filesystem is not touched, don't use the filesystem
playground/sandbox
2. If the filesystem is not touched, don't specify the `cwd`
3. If the command is short, don't bother wrapping it in `pipeline()`
4. If the command doesn't have quotes, don't bother with a `r#"..."#`
raw string
Part of #8670.
