For a lot of these I think idempotency is the wrong angle to look at it. For example, the problem with mkdir foo is not that it's non-idempotent, it's that (in

For a lot of these I think idempotency is the wrong angle to look at it. For example, the problem with mkdir foo is not that it's non-idempotent, it's that (in most cases) the directory already existing is not an error to begin with: it still satisfies the same post-condition you desired. To put it another way, you're usually trying to say "ensure this directory exists", not "ensure you create this directory", and as such, unless you're really trying to test directory creation, mkdir without -p is a semantic bug regardless of whether you need to run it multiple times.