tests: Add testcase for multiple inheritance.

tests/basics/class_inherit_mul.py

@@ -0,0 +1,37 @@
+class A:
+    def __init__(self, x):
+        print('A init', x)
+        self.x = x
+
+    def f(self):
+        print(self.x)
+
+    def f2(self):
+        print(self.x)
+
+class B:
+    def __init__(self, x):
+        print('B init', x)
+        self.x = x
+
+    def f(self):
+        print(self.x)
+
+    def f3(self):
+        print(self.x)
+
+
+class Sub(A, B):
+    def __init__(self):
+        A.__init__(self, 1)
+        B.__init__(self, 2)
+        print('Sub init')
+
+    def g(self):
+        print(self.x)
+
+o = Sub()
+print(o.x)
+o.f()
+o.f2()
+o.f3()