I suppose that @serhiy-storchaka would be a better candidate than me to review this change.

I replaces tests with tests with deterministic result (when all sets can be strictly ordered). I do not know what to do with testing non-orderable sets, which perhaps was the purpose of the original set. Maybe we should test the actual result against multiple expected results.

@serhiy-storchaka: Are you ok with this change? Does it make test_pprint better?

Maybe we should test the actual result against multiple expected results.

Maybe add a test with a set of 2 strings and check if the repr() is in one of the two possible outputs?

I thought that @rhettinger should make the decision, but he removed himself.

Well, I propose the following plan:

1. Use strings instead of integers to make the iteration order and the repr non-deterministic.
2. Test the result against all possible outcomes.
3. To keep the number of variants (which grows exponentially) in reasonable limits, use sets with not more than 2 items.
4. Most cases should be tested to produce single-line and multi-line results. To make the result multi-line, use smaller width value or longer strings, or both.

@serhiy-storchaka

1. Thanks, I was not familiar with this implementation detail:

Actually, in the multiline case, the elements of the innermost frozensets are always sorted.

I've tried locally with these cases removed and while true; do ./python.exe -m test test_pprint -m test_set_of_sets_reprs -v; done showed that this is actually true.

2. I've also added repr case.
3. Added the case for multiline result with single-line frozensets 👍

However, it does not work the same way as fully multiline case.

For example, this result is expected:

frozenset({frozenset({'regular string', 'other string'}),
           frozenset({'third string', 'one more string'})})

Traceback:

» ./python.exe -m test --forever test_pprint -m test_set_of_sets_reprs
Using random seed: 1266073671
0:00:00 load avg: 2.92 Run tests sequentially
0:00:00 load avg: 2.92 [  1] test_pprint
test test_pprint failed -- Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython2/Lib/test/test_pprint.py", line 695, in test_set_of_sets_reprs
    check(
  File "/Users/sobolev/Desktop/cpython2/Lib/test/test_pprint.py", line 692, in check
    self.assertIn(res, [textwrap.dedent(i).strip() for i in invariants])
AssertionError: "frozenset({frozenset({'regular string', 'other string'}),\n           frozenset({'third string', 'one more string'})})" not found in ["frozenset({frozenset({'other string', 'regular string'}),\n           frozenset({'third string', 'one more string'})})", "frozenset({frozenset({'other string', 'regular string'}),\n           frozenset({'one more string', 'third string'})})", "frozenset({frozenset({'third string', 'one more string'}),\n           frozenset({'other string', 'regular string'})})", "frozenset({frozenset({'third string', 'one more string'}),\n           frozenset({'regular string', 'other string'})})"]

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