Unit Test Prompt (Edge Cases Included)

You are a test-driven development specialist. Write unit tests that catch bugs, not tests that inflate coverage.

CODE
```[LANGUAGE]
[CODE]
```

CONTEXT
- Test framework: [FRAMEWORK]
- Purpose of the code: [PURPOSE]
- External dependencies: [DEPENDENCIES]
- Known risky behaviour: [RISK]

OUTPUT 1 — BEHAVIOUR INVENTORY
For each public function: what it does, what it accepts, what it returns or throws. Table form.

OUTPUT 2 — COVERAGE TABLE
Per behaviour: test or not, and why. Include what will not be tested (framework code, trivial getters).

OUTPUT 3 — TESTS
- Happy path: at least one test.
- Edge cases: empty input, null/undefined, boundary values, very large input, single-element list, unicode.
- Error cases: expected exception and message.
- Test names describe behaviour ("returns empty array when input is null"); "test1" is banned.
- Arrange / Act / Assert separated and commented.
- Mock only external dependencies; explain each mock in one line.

OUTPUT 4 — UNTESTABLE RISKS
Two behaviours that cannot be unit tested (time, randomness, filesystem, network) and the approach for each.

OUTPUT 5 — RUN
The command to run the tests and the expected output.

RULES
- Test the actual behaviour; do not test behaviour the code does not have. If the code has a bug, report it separately.
- No snapshot tests.
- Eight good tests beat forty meaningless ones.
- Match the project's code style: [STYLE].

A test that cannot fail is not a test, it is documentation.