Add unit tests for lib/util.js

[gendelbendel]

Commits:

• Phase 1: Initial phase, already committed before this pull request. Empty skeleton tests.
• Phase 2: Add basic unit tests that we believe should pass. These are trivial and not quite catered to our use case.
• Phase 3: Add unit tests with the observed behavior failing
• Phase 4: Add more unit tests, to explore functionality across multiple other use cases, including different data types with their expected behaviors. No more failures observed.
• Phase 5: Add more unit tests, in which more failures begin to occur. It revolves around duplicate entries, so we've found the bug.
• Phase 6: Fix the bug, observe all tests passing.