Improve test coverage

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (71990a9) 60.97% compared to head (e66ffbc) 82.35%.

Files	Patch %	Lines
chatminer/chatparsers.py	87.50%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #123 +/- ## =========================================== + Coverage 60.97% 82.35% +21.37% =========================================== Files 2 1 -1 Lines 328 289 -39 =========================================== + Hits 200 238 +38 + Misses 128 51 -77 ``` | [Flag](https://app.codecov.io/gh/joweich/chat-miner/pull/123/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jonas+Weich) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/joweich/chat-miner/pull/123/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jonas+Weich) | `82.35% <87.50%> (+21.37%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jonas+Weich#carryforward-flags-in-the-pull-request-comment) to find out more.

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