[New-bugs-announce] [issue35687] The unittest module diff is missing/forgetting/not putting newline before + and ? for some inputs

[Addons Zz]

New submission from Addons Zz <addonszz at outlook.com>:

Create this program and run with `Python 3.6.3`:
```python
import unittest

class StdErrUnitTests(unittest.TestCase):

    def test_function_name(self):
        expected = "testing.main_unit_tests.test_dictionaryBasicLogging:416 - dictionary\n" \
                "testing.main_unit_tests.test_dictionaryBasicLogging:417 - dictionary {1: 'defined_chunk'}"

        actual = "15:49:35:912.348986 - testing.main_unit_tests - dictionary\n" \
                "15:49:35:918.879986 - testing.main_unit_tests - dictionary {1: 'defined_chunk'}"

        self.assertEqual(expected, actual)

if __name__ == '__main__':
    unittest.main()
```

### Actual output

```diff
F
======================================================================
FAIL: test_function_name (__main__.StdErrUnitTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\bug_assert_unittests.py", line 13, in test_function_name
    self.assertEqual(expected, actual)
AssertionError: "testing.main_unit_tests.test_dictionaryBa[114 chars]nk'}" != "15:49:35:912.348986 - testing.main_unit_t[94 chars]nk'}"
- testing.main_unit_tests.test_dictionaryBasicLogging:416 - dictionary
- testing.main_unit_tests.test_dictionaryBasicLogging:417 - dictionary {1: 'defined_chunk'}+ 15:49:35:912.348986 - testing.main_unit_tests - dictionary
+ 15:49:35:918.879986 - testing.main_unit_tests - dictionary {1: 'defined_chunk'}

----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (failures=1)
```

### Expected output

```diff
F
======================================================================
FAIL: test_function_name (__main__.StdErrUnitTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\bug_assert_unittests.py", line 13, in test_function_name
    self.assertEqual(expected, actual)
AssertionError: "testing.main_unit_tests.test_dictionaryBa[114 chars]nk'}" != "15:49:35:912.348986 - testing.main_unit_t[94 chars]nk'}"
- testing.main_unit_tests.test_dictionaryBasicLogging:416 - dictionary
- testing.main_unit_tests.test_dictionaryBasicLogging:417 - dictionary {1: 'defined_chunk'}
+ 15:49:35:912.348986 - testing.main_unit_tests - dictionary
+ 15:49:35:918.879986 - testing.main_unit_tests - dictionary {1: 'defined_chunk'}

----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (failures=1)
```

### Differences between actual and expected output

```diff
@@ -7,7 +7,8 @@
     self.assertEqual(expected, actual)
 AssertionError: "testing.main_unit_tests.test_dictionaryBa[114 chars]nk'}" != "15:49:35:912.348986 - testing.main_unit_t[94 chars]nk'}"
 - testing.main_unit_tests.test_dictionaryBasicLogging:416 - dictionary
-- testing.main_unit_tests.test_dictionaryBasicLogging:417 - dictionary {1: 'defined_chunk'}+ 15:49:35:912.348986 - testing.main_unit_tests - dictionary
+- testing.main_unit_tests.test_dictionaryBasicLogging:417 - dictionary {1: 'defined_chunk'}
++ 15:49:35:912.348986 - testing.main_unit_tests - dictionary
 + 15:49:35:918.879986 - testing.main_unit_tests - dictionary {1: 'defined_chunk'}
```

This kind of bug frequently happens. On this case, it is not putting a new line before the `+`. Other cases, it is not putting a new line before the `?`.

----------
components: Tests, Windows
messages: 333258
nosy: addons_zz, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: The unittest module diff is missing/forgetting/not putting newline before + and ? for some inputs
type: behavior
versions: Python 3.6

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35687>
_______________________________________