feat: clean up and improve (#8)

[tkrop]

This pull request cleans up the code, especially with respect to error handling, fixes some minor bugs, and improves the test code.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.00% (target: -1.00%)	✅ 100.00% (target: 80.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (8e48841)	319	319	100.00%
Head commit (95222b3)	338 (+19)	338 (+19)	100.00% (+0.00%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#8)	41	41	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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