Add tests for every database handler

[michalsn]

Description
This PR adds tests for all database handlers.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

Okay, seems like I will have to set up a local docker image to resolve this.

[coveralls]

Pull Request Test Coverage Report for Build 12515475471

Details

• 25 of 25 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+3.1%) to 90.501%

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Totals
Change from base Build 10938598555:	3.1%
Covered Lines:	524
Relevant Lines:	579

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💛 - Coveralls

[michalsn]

Thank you @paulbalandan!