Question

I created a cooperation of 4 classes (Python).

class A:
    ## A, B, C are nested classes of A
    class B:
        ...
    class C:
        ...
    class D:
        ...
    ## example methods
    def newB(self):
        return self.B()
    def newC(self):
        return self.C(self.newB())

I wrote 60 test-methods in 4 test-cases and this was hard work.

Because B, C, D do not offer much behaviour, the A, B, C, D classes shall be subclassed to add new behaviour.

The Problem:

I wrote much test code to ensure that A, B, C, D cooperate right.
If I subclass A, B, C, D to A2, B2, C2, D2 I will need to test the behaviour of A2, B2, C2, D2 in the same way I tested A, B, C, D.

How do I do this?

1. subclass all unittests every time I create a new subclass of Database?
2. generate the test cases and a suite by a method?
3. …

What would be your practices to assure that the subclassed Database works correctly and there is no mistake in it?

Given: unittests, the classes of Database and your subclass(es)

Tests that exist now:

class TestA(unittest.TestCase):
    A = A
    def setUp(self):
        self.a = self.A()
    def test_something(self):
        ...

class MockB(A.B):
    ...
class AWithMock(A):
    B = MockB
class TestAWithMock(TestA):
    A = AWithMock
    def setUp(self):
        self.a = self.A()
    def test_something_new(self):
        ...

class MockB2(A.B):
    ...
class MockC2(A.C):
    ...
class MockD2(A.D):
    ...
class TestWithMock(unittest.TestCase):
    def test_b(self):
        b = MockB2()
        ...
    def test_c(self):
        ...
    def test_d(self):
        ...

Answer 1

import unittest
class TestCaseA(unittest.TestCase):
    def setUp(self):
        self.thing = A()

    def test_does_x():
        self.assertTrue(self.thing.does_x())

Now define a subclass A2:

class A2(A):
    ...

I would subclass your testcase but only override the setUp/setup method as the rest of the API of the subclass A2 should be consistent with A.

So your test subclass would be just:

class TestA2(TestCaseA):
    def setUp(self):
        self.thing = A2()