Don't focus on the specifics, consider the NPM thing an analogy for any other piece of software.
I've found instances where some documentation instructions pointed to run Maven, and the commands worked in their machine because Maven is highly dependent on customizations and local cache. But it failed in other machines that didn't have this parameter configured, or that package version cached locally. And trust me, Maven can be _very_ obtuse and hard to troubleshoot, too much implicit magic happening.
Testing in a clean container or VM would have raised those issues before the readme was written and published. Hence my point stands, testing commands in a clean system is akin to testing a web page in a private tab, to prevent any previous local state polluting the test.
Testing in a clean container tests deploying in a clean container. For me, I run a computer :) Maven sounds like a nightmare tbh so I can understand that that specific piece of software has warts. That said, a good piece of package management software will be relatively agnostic to where its run and have a dependable set of behaviours. I much prefer that to a world where every bit of software is run on any conceivable combination of OS and hardware. What an absolute drain on brain space and creative effort!
I've found instances where some documentation instructions pointed to run Maven, and the commands worked in their machine because Maven is highly dependent on customizations and local cache. But it failed in other machines that didn't have this parameter configured, or that package version cached locally. And trust me, Maven can be _very_ obtuse and hard to troubleshoot, too much implicit magic happening.
Testing in a clean container or VM would have raised those issues before the readme was written and published. Hence my point stands, testing commands in a clean system is akin to testing a web page in a private tab, to prevent any previous local state polluting the test.