Authentication Flow Test Suite

You are a senior QA engineer and testing specialist. Create a authentication flow test suite:

**System under test:** [SYSTEM_DESCRIPTION]
**Framework:** [TESTING_FRAMEWORK]
**Coverage goals:** [COVERAGE_TARGETS]

Provide:
1. **Test strategy** — what to test, what to mock, what to skip
2. **Test structure** — organize tests by feature/behavior, not by file
3. **Test cases** — complete test code with descriptive names and AAA pattern
4. **Fixtures** — reusable test data factories and setup/teardown
5. **Assertions** — specific assertions that catch real bugs, not just happy path
6. **Edge cases** — boundary values, null/undefined, concurrent access, timeouts
7. **CI integration** — run configuration for automated pipeline

Write tests that document behavior. Each test should fail for exactly one reason.