Included more unit test cases for transformation functions

[github-actions[bot]]

:bookmark_tabs: PR details: This PR updates the main repository branch with new test cases for transformers.py auxiliar module. The module has useful functions that handle all Spark transformation methods applied on data sources in Glue job.

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:link: Chained issues This PR eventually will close the following issues:

• 69

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  :hammer: Tasks done:

• Included new fixtures with sample DataFrames to be testes
• Included new fixtures with DataFrames that are results of transformation methods on transformers.py file

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  :heavy_check_mark: Checklist:

• [x] New code followed the best practices
• [x] New features were tested properly
• [x] There is no chance new features would compromise the project

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +3.38 :tada:

Comparison is base (3a48b6f) 96.61% compared to head (94764f3) 100.00%.

:exclamation: Current head 94764f3 differs from pull request most recent head 1846dc7. Consider uploading reports for the commit 1846dc7 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #76 +/- ## =========================================== + Coverage 96.61% 100.00% +3.38% =========================================== Files 4 5 +1 Lines 118 356 +238 =========================================== + Hits 114 356 +242 + Misses 4 0 -4 ``` | [Impacted Files](https://codecov.io/gh/ThiagoPanini/terraglue/pull/76?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Thiago+Panini) | Coverage Δ | | |---|---|---| | [app/src/transformers.py](https://codecov.io/gh/ThiagoPanini/terraglue/pull/76?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Thiago+Panini#diff-YXBwL3NyYy90cmFuc2Zvcm1lcnMucHk=) | `100.00% <100.00%> (ø)` | | | [app/tests/conftest.py](https://codecov.io/gh/ThiagoPanini/terraglue/pull/76?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Thiago+Panini#diff-YXBwL3Rlc3RzL2NvbmZ0ZXN0LnB5) | `100.00% <100.00%> (+5.55%)` | :arrow_up: | | [app/tests/helpers/dataframes.py](https://codecov.io/gh/ThiagoPanini/terraglue/pull/76?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Thiago+Panini#diff-YXBwL3Rlc3RzL2hlbHBlcnMvZGF0YWZyYW1lcy5weQ==) | `100.00% <100.00%> (+5.26%)` | :arrow_up: | | [app/tests/test\_helpers.py](https://codecov.io/gh/ThiagoPanini/terraglue/pull/76?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Thiago+Panini#diff-YXBwL3Rlc3RzL3Rlc3RfaGVscGVycy5weQ==) | `100.00% <100.00%> (ø)` | | | [app/tests/test\_transformers.py](https://codecov.io/gh/ThiagoPanini/terraglue/pull/76?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Thiago+Panini#diff-YXBwL3Rlc3RzL3Rlc3RfdHJhbnNmb3JtZXJzLnB5) | `100.00% <100.00%> (+20.00%)` | :arrow_up: |

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