trac 10849: add doctests for fix to number field element comparison

Author: burcin

src/sage/symbolic/expression.pyx

@@ -2956,6 +2956,16 @@ cdef class Expression(CommutativeRingElement):
             sage: g = expand(iterkate(7))
             sage: g.nops()
             480
+
+        Check if :trac:`10849` is fixed::
+
+            sage: t = I.pyobject().parent()(-1/2)
+            sage: t > 0
+            False
+            sage: t = I*x-1/2; t
+            I*x - 1/2
+            sage: t.subs(x=I*x).subs(x=0).is_positive()
+            False
         """
         return (<Element>left)._cmp(right)