[FEATURE] Increase test coverage by including test cases for manager and glue modules

[ThiagoPanini]

🚀 Feature needed:
This request embraces the increase of the test coverage for the project by including new test cases for features presented on both manager.py and glue.py module. The manager module holds the SparkETLManager class with some useful methods that enable an enhancement on Spark usage on both local mode and glue mode.

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🏆 Feature benefits:
With this new features, user would:

• Ensure features are properly tested
• Increase the project coverage

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📚 Complexity:
The best category that fits into the development of this new feature is:

• High complexity

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💡 Ideas on how to develop it:
To develop this new feature, would be possible to:

• Create a new test script called test_manager_module.py
• Add new fixtures, if applicable
• Create fake Spark DataFrames to be used on tests