Python unittest swaps object instances between tests

I am writing some unit tests in Python and it seems that my tests are somehow sharing objects between test functions, which seems strange. So, I have something like:

import unittest 

class TestMyMethods(unittest.TestCase):

    def test_create(self):
        c = MyClass()
        c.create_customer('Luca')
        self.assertEqual(len(c.data), 1)

    def test_connect(self):
        c = MyClass()
        c.connect_customer('Angela', 'Peter')
        self.assertEqual(len(c.data), 2)

      

        
        
        
      

    

If I comment on either test the other will pass, but both will fail together. On the exam, it seems that the object is being c

persisted between the two test functions, but why should that be? New instances are created in the function. Is this some "feature" out of the box unittest

?

from collections import defaultdict
class MyClass(object):
    def __init__(self):
        self.data = defaultdict()

    def create_customer(self, cust):
        if cust not in self.data:
            self.data[cust] = list()

    def connect_customer(self, a, b):
        if a not in self.data:
            self.data[a] = list()

        if b not in self.data:
            self.data[b] = list()

        self.data[a].append(b)

      

        
        
        
      

    

OK, this is weird. I looked at history and before that I got this:

class MyClass(object):
    def __init__(self, data=defaultdict()):
        self.data = data

      

        
        
        
      

    

And the tests didn't work when I initialized this. It works now. I must have deleted this without tracking.

Does anyone know why this is not working? but the execution is self.data = defaultdict()

fine.