fix test case in Py3

tests/run/complex_numbers_T305.pyx

@@ -21,7 +21,7 @@ def test_arithmetic(double complex z, double complex w):
     >>> test_arithmetic(5-10j, 3+4j)
     ((5-10j), (-5+10j), (8-6j), (2-14j), (55-10j), (-1-2j))
     """
-    return +z, -z, z+w, z-w, z*w, z/w
+    return +z, -z+0, z+w, z-w, z*w, z/w
 
 @cython.cdivision(False)
 def test_div_by_zero(double complex z):