This command
cd $(mktemp -d)
mkdir a "a b"
complete -C": "
prints
a b/
a/
which is wrong ordering.
Usually the trailing slash should not be compared.
Fix this by always sorting slashes first. Not sure if this is correct
for middle slashes but I couldn't find a case where it matters.
Closes#12695
Using `assert_eq!` instead of `assert!` has the advantage that when the
assertion fails, the debug representation of both sides will be shown,
which can provide more information about the failure than only seeing
that the assertion failed.
Part of #12336
