test: add unit tests for library orientation

[rohank63]

Resolves #83

Type of change

Please delete options that are not relevant.

• [X] Bug fix (non-breaking change which fixes an issue)
• [X] Extensive Unit Testing
• [X] Documentation update

Checklist

Please carefully read these items and tick them off if the statements are true or do not apply.

• [X] I have performed a self-review of my own code
• [X] My code follows the existing coding style, lints and generates no new warnings
• [X] I have added type annotations to all function/method signatures, and I have added type annotations for any local variables that are non-trivial, potentially ambiguous or might otherwise benefit from explicit typing.
• [X] I have commented my code in hard-to-understand areas
• [X] I have added ["Google-style docstrings"] to all new modules, classes, methods/functions or updated previously existing ones
• [X] I have added tests that prove my fix is effective or that my feature works
• [X] New and existing unit tests pass locally with my changes and I have not reduced the code coverage relative to the previous state
• [X] I have updated any sections of the app's documentation that are affected by the proposed changes

[codecov-commenter]

Codecov Report

Base: 100.00% // Head: 99.56% // Decreases project coverage by -0.43% :warning:

Coverage data is based on head (32465c4) compared to base (5922441). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #91 +/- ## =========================================== - Coverage 100.00% 99.56% -0.44% =========================================== Files 11 12 +1 Lines 692 921 +229 =========================================== + Hits 692 917 +225 - Misses 0 4 +4 ``` | [Impacted Files](https://codecov.io/gh/zavolanlab/htsinfer/pull/91?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zavolanlab) | Coverage Δ | | |---|---|---| | [htsinfer/exceptions.py](https://codecov.io/gh/zavolanlab/htsinfer/pull/91/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zavolanlab#diff-aHRzaW5mZXIvZXhjZXB0aW9ucy5weQ==) | `100.00% <100.00%> (ø)` | | | [htsinfer/get\_read\_orientation.py](https://codecov.io/gh/zavolanlab/htsinfer/pull/91/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zavolanlab#diff-aHRzaW5mZXIvZ2V0X3JlYWRfb3JpZW50YXRpb24ucHk=) | `98.24% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zavolanlab). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zavolanlab)

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[uniqueg]

Good stuff - thanks a lot @rohank63!