Unit test review

Review unit tests to ensure that each test is checking something that we need to be true to rely on the software, and brainstorm additional tests if we're not covering important corner cases.

Begin by locating the repository's unit-test files and reviewing what each test actually guarantees about the software. Identify tests that do not assert required behavior and important untested corner cases; done means the suite clearly checks relied-upon behavior and covers the agreed cases.

Written by the indexing model from the issue text.