How to test an `npm publish` result, without actually publishing to NPM?

Question

One common problem I have, is that sometimes my .npmignore file is too aggressive, and I ignore files that I actually will to include in the NPM tarball.

My question is

Answer 1

(2019 answer)

Simply run

npm pack

In npm 6 and up, this will display what files are going to be uploaded and create a tar ball in the current directory.