Add test for class with sub and rsub.

tests/snippets/subtraction.py

@@ -0,0 +1,21 @@
+assert 5 - 3 == 2
+
+class Complex():
+    def __init__(self, real, imag):
+        self.real = real
+        self.imag = imag
+
+    def __repr__(self):
+        return "Com" + str((self.real, self.imag))
+
+    def __sub__(self, other):
+        return Complex(self.real - other, self.imag)
+
+    def __rsub__(self, other):
+        return Complex(other - self.real, -self.imag)
+
+    def __eq__(self, other):
+        return self.real == other.real and self.imag == other.imag
+
+assert Complex(4, 5) - 3 == Complex(1, 5)
+assert 7 - Complex(4, 5) == Complex(3, -5)