I’ve noticed some strange behaviour when setting a test suite’s _tests attribute to empty, and then attempting to add tests to it again as part of a loop.

I have to essentially reinitialise a test suite’s contents as part of running my whole test suite in a loop. I’ve found that I can’t just call the same test suite again, iteratively, and so I reinitialise it.

Before entering my loop, I have a list of tests my_tests.

runner = unittest.TextTestRunner()
my_suite = unittest.TestSuite(my_tests)
for i in range(2):
  result = runner.run(my_suite)

  print(f"{i} Number of tests, after running tests: suite suite length {my_suite.countTestCases()} test object     {my_tests}")

  unittest.registerResult(result)
  # Empty test suite and re-add tests
  my_suite._tests = []

  print(my_suite.__dict__)
  
  my_suite.addTests(my_tests)
  print(my_suite.__dict__)

  print(f"{i} Number of tests, after reinitialising suite: suite length {my_suite.countTestCases()} test object {my_tests}")
  

and I get the following output

----------------------------------------------------------------------
Ran 1 test in 0.000s

OK
0 Number of tests, after running tests: suite length 1 test object [<single_node_tests.SingleNodeTest testMethod=test_basic>]
{'_tests': [], '_removed_tests': 1}
{'_tests': [<single_node_tests.SingleNodeTest testMethod=test_basic>], '_removed_tests': 1}

0 Number of tests, after reinitilising suite:suite length 2 test object [<single_node_tests.SingleNodeTest testMethod=test_basic>]

.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK
1 Number of tests, after running tests: suite length 2 test object [<single_node_tests.SingleNodeTest testMethod=test_basic>]
{'_tests': [], '_removed_tests': 2}
{'_tests': [<single_node_tests.SingleNodeTest testMethod=test_basic>], '_removed_tests': 2}
1 Number of tests, after reinitilising suite:suite length 3 test object [<single_node_tests.SingleNodeTest testMethod=test_basic>]

so the number of tests in the test suite is actually increasing over iterations, despite the list being set to an empty list. seen in suite length 1 -> suite length 2 -> suite length 3

I tried and succeeded in resolving this with the following:

I added:

my_suite.removed_tests = 0 

and then found that the reported suite length stayed at 1, over all iterations.

I really just don’t understand why the removed_test count would affect the behaviour of adding tests to a suite, which is reported to be empty?