numeric sort with unique option does not show 0!

I have a file with many redundant numbers in each row. Imagine something like the below:

echo "10
9
5
6
4
cell
3
2
0
7
0
1" > test

When I use sort -un test I get the following output:

cell
1
2
3
4
5
6
7
9
10

while I expect the below (I mean 0 as a first row of the output):

0
1
2
3
4
5
6
7
9
10

Applying the sort -n and then redirecting to uniq doesn't make such a mess, however, it shows the non-numeric lines. Is there any way to just use the sort with -nu to get 0 at the first line instead of an alphanumeric token?