old_contents: class baz:
    A = 8
  class bar(baz):
    x = 0
    def test(self):
      return 'test in bar'
    def test1(self,x):
      return x*'test1'
  
  class truc:
      machin = 99
      
  class foo(bar,truc):
   def test(self):
    return 'test in foo'
   def test2(self):
     return 'test2'
  
  obj = foo()
  assert str(bar.test)=="<function bar.test>"
  assert str(obj.test)=="<bound method foo.test of <object 'foo'>>"
  assert obj.A == 8
  assert obj.x == 0
  assert obj.test()=='test in foo'
  assert obj.test1(2)=='test1test1'
  assert obj.test2()=='test2'
  
  #there is an error here, displayed on web console
  assert obj.machin == 99
  
  print('passed all tests..')
  
new_contents: class baz:
    A = 8
  class bar(baz):
    x = 0
    def test(self):
      return 'test in bar'
    def test1(self,x):
      return x*'test1'
  
  class truc:
      machin = 99
      
  class foo(bar,truc):
   def test(self):
    return 'test in foo'
   def test2(self):
     return 'test2'
  
  obj = foo()
  assert str(bar.test)=="<function bar.test>"
  assert obj.A == 8
  assert obj.x == 0
  assert obj.test()=='test in foo'
  assert obj.test1(2)=='test1test1'
  assert obj.test2()=='test2'
  
  #there is an error here, displayed on web console
  assert obj.machin == 99
  
  class stack(list):
  
      def dup(self):
          if len(self):
              self.append(self[-1])
  
  x = stack([1,7])
  assert str(x)=='[1,7]'
  x.dup()
  assert str(x)=='[1,7,7]'
  
  print('passed all tests..')
  
subject: Add more tests to test_classes.py