Ensure log truncations are at nearest newline after truncation size

[ccrighton]

I reviewed #41 and found that it didn't behave consistently.

The behaviour expected is to truncate the file at the new line immediately after the truncation break point is reached. This means the truncation is always at least as small as requested. There is also cases at the start and end of file in #41 that do not behave rationally.

I would recommend this PR instead of #41.

Run the test cases with:
python -m unittest tests/*_test.py -v

Here is the test case results from #41 using the unit tests from this PR:

.FFFFFFF
======================================================================
FAIL: test_truncate_after_last_newline (__main__.TestUtils)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/charlie/PycharmProjects/phew/tests/logging_test.py", line 37, in test_truncate_after_last_newline
    self.assertEqual("", l.read(4))
AssertionError: '' != '2021'
+ 2021

======================================================================
FAIL: test_truncate_after_last_newline_no_newline_at_eof (__main__.TestUtils)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/charlie/PycharmProjects/phew/tests/logging_test.py", line 99, in test_truncate_after_last_newline_no_newline_at_eof
    self.assertEqual("", l.read(4))
AssertionError: '' != '2021'
+ 2021

======================================================================
FAIL: test_truncate_before_first_newline (__main__.TestUtils)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/charlie/PycharmProjects/phew/tests/logging_test.py", line 60, in test_truncate_before_first_newline
    self.assertEqual(size, truncated_size + 55)
AssertionError: 8724 != 7785

======================================================================
FAIL: test_truncate_between_first_and_last_newlines (__main__.TestUtils)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/charlie/PycharmProjects/phew/tests/logging_test.py", line 50, in test_truncate_between_first_and_last_newlines
    self.assertEqual(size, truncated_size + 63)
AssertionError: 4000 != 4312

======================================================================
FAIL: test_truncate_on_newline (__main__.TestUtils)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/charlie/PycharmProjects/phew/tests/logging_test.py", line 69, in test_truncate_on_newline
    self.assertEqual("2021-01-01 00:02:21", l.read(19))
AssertionError: '2021-01-01 00:02:21' != '2021-01-01 00:09:32'
- 2021-01-01 00:02:21
?                 ---
+ 2021-01-01 00:09:32
?                +++


======================================================================
FAIL: test_truncate_to_zero (__main__.TestUtils)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/charlie/PycharmProjects/phew/tests/logging_test.py", line 88, in test_truncate_to_zero
    self.assertEqual("", l.read(4))
AssertionError: '' != '2021'
+ 2021

======================================================================
FAIL: test_truncate_to_zero_no_newline_at_eof (__main__.TestUtils)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/charlie/PycharmProjects/phew/tests/logging_test.py", line 109, in test_truncate_to_zero_no_newline_at_eof
    self.assertEqual("", l.read(4))
AssertionError: '' != '2021'
+ 2021

----------------------------------------------------------------------
Ran 8 tests in 0.007s

FAILED (failures=7)

[macifell]

It's great to see a more complete solution to this!

I tried running the tests on your branch, but a few of them failed.

test_truncate_after_end_of_file (tests.logging_test.TestUtils.test_truncate_after_end_of_file) ... ok
test_truncate_after_last_newline (tests.logging_test.TestUtils.test_truncate_after_last_newline) ... ok
test_truncate_after_last_newline_no_newline_at_eof (tests.logging_test.TestUtils.test_truncate_after_last_newline_no_newline_at_eof) ... ok
test_truncate_before_first_newline (tests.logging_test.TestUtils.test_truncate_before_first_newline) ... FAIL
test_truncate_between_first_and_last_newlines (tests.logging_test.TestUtils.test_truncate_between_first_and_last_newlines) ... FAIL
test_truncate_on_newline (tests.logging_test.TestUtils.test_truncate_on_newline) ... FAIL
test_truncate_to_zero (tests.logging_test.TestUtils.test_truncate_to_zero) ... ok
test_truncate_to_zero_no_newline_at_eof (tests.logging_test.TestUtils.test_truncate_to_zero_no_newline_at_eof) ... ok

======================================================================
FAIL: test_truncate_before_first_newline (tests.logging_test.TestUtils.test_truncate_before_first_newline)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tests/logging_test.py", line 60, in test_truncate_before_first_newline
    self.assertEqual(size, truncated_size + 55)
AssertionError: 8724 != 8675

======================================================================
FAIL: test_truncate_between_first_and_last_newlines (tests.logging_test.TestUtils.test_truncate_between_first_and_last_newlines)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tests/logging_test.py", line 50, in test_truncate_between_first_and_last_newlines
    self.assertEqual(size, truncated_size + 63)
AssertionError: 4000 != 4031

======================================================================
FAIL: test_truncate_on_newline (tests.logging_test.TestUtils.test_truncate_on_newline)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tests/logging_test.py", line 69, in test_truncate_on_newline
    self.assertEqual("2021-01-01 00:02:21", l.read(19))
AssertionError: '2021-01-01 00:02:21' != '2021-01-01 00:02:22'
- 2021-01-01 00:02:21
?                   ^
+ 2021-01-01 00:02:22
?                   ^


----------------------------------------------------------------------
Ran 8 tests in 0.003s

FAILED (failures=3)

[ccrighton]

@macifell thanks for the review, I'll take a look.

[ccrighton]

@macifell The issue was that the tests were sensitive to the line ending. I've created a .gitattributes file to ensure that the log files have LF only. I rewrote the history of that branch.

[macifell]

Thanks @ccrighton! The tests all pass for me now.