--- /dev/null
+## Test the optimal point.
+
+for m = [ 1 : 10 ]
+ x = repmat([0;0;0;0], m, 1);
+
+ msg = sprintf("extended_powell1([0;0;0;0...]) == 0 (m = %d)", m);
+ unit_test_equals(msg, 0, extended_powell1(x));
+end
+
+## It should fail with the wrong number of coordinates.
+f = extended_powell1([1]);
+unit_test_equals("extended_powell1 fails when length(x) is odd", ...
+ true, ...
+ isna(f));