Generate Unit Tests

You are a testing expert. Write comprehensive unit tests for the following code.

Code Under Test

{{CODE}}

Function/Module Name

{{FUNCTION_NAME}}

Test Framework

{{TEST_FRAMEWORK}}

Language

{{LANGUAGE}}

Test Generation Guidelines

1. Test Categories

Generate tests for each of these categories:

Happy Path Tests

• Test the primary use case with valid inputs
• Test with typical, expected data
• Verify the correct return value and side effects

Error Cases

• Test with invalid inputs (wrong type, format, range)
• Test error messages are descriptive
• Test that errors don't leave the system in a corrupt state
• Test async rejection handling

Edge Cases

• Empty inputs (empty string, empty array, null, undefined)
• Boundary values (0, -1, MAX_SAFE_INTEGER, Number.EPSILON)
• Unicode and special characters
• Very large inputs
• Concurrent invocations (if applicable)

State Transitions

• Test before and after state changes
• Test idempotency (calling twice produces same result)
• Test cleanup/teardown behavior

2. Test Structure

For each test:

• Arrange: Set up preconditions and inputs
• Act: Execute the function under test
• Assert: Verify the output and side effects
• Use descriptive test names: "should [expected behavior] when [condition]"

3. Mocking Strategy

• Mock external dependencies (APIs, databases, file system)
• Use the simplest mock possible (stub > spy > mock)
• Verify mock interactions only when the interaction is the behavior being tested
• Reset mocks between tests

4. Test Quality Checks

• Each test should test one thing
• Tests should be independent (no shared state between tests)
• Tests should be deterministic (no randomness, no time-dependence)
• Tests should be fast (mock I/O, avoid real network calls)
• Test names should document the expected behavior

Output Format

Provide complete, runnable test file with:

1. Imports and setup
2. Organized test suites (describe blocks)
3. Individual test cases (it/test blocks)
4. Helper functions and test fixtures
5. Comments explaining non-obvious test cases
6. Coverage report expectation (which lines/branches are covered)