Enable -Werror for unit tests and fix resulting compiler warnings

[thulasiramk-2310]

Goal

Enable -Werror for all unit test builds and fix the warnings that appear when compiling tests with this flag enabled.

Why

Unit tests previously did not compile with -Werror, which allowed several warnings to accumulate unnoticed.
Applying warnings-as-errors improves build hygiene, enforces consistency with the main library build, and prevents future regressions.

How

Build System

• Updated CMakeLists.txt to apply -Werror to all unit test targets when UNSAFE_TREAT_WARNINGS_AS_ERRORS=ON is set.

Warning Fixes

• tests/unit/s2n_safety_test.c

  • Initialized a local buffer to resolve a maybe-uninitialized warning.

• tests/unit/s2n_tls12_handshake_test.c

  • Replaced invalid array-to-array comparisons with memcmp().

• tests/unit/s2n_tls13_handshake_state_machine_test.c

  • Replaced array comparisons with proper memcmp() checks.

Verification

• Rebuilt the entire project with strict warning settings to ensure no further warnings remain.

Callouts

• This enforcement uses the existing UNSAFE_TREAT_WARNINGS_AS_ERRORS mechanism to keep the change opt-in, as requested in the issue discussion.
• If maintainers prefer applying this unconditionally, I can update the PR accordingly.

Testing

Built and tested with:

cmake -DUNSAFE_TREAT_WARNINGS_AS_ERRORS=ON ..
make -j

Verified:

• 100% of unit tests pass (280 tests, 0 failures)
• All warnings resolved
• No behavioral regressions introduced

Related

Resolves #5650

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[maddeleine]

Looks like there's also a failure on mac builds. I think you probably just need to add an if-def S2N_CLONE_SUPPORTED around the s2n_unit_test_clone_child_process function to get those builds to pass.

[maddeleine]

This is not the correct place for this change. The fork_generation_number_test is the testfile that is causing the issue.

[thulasiramk-2310]

Thanks for pointing that out — I’ll move the guard to fork_generation_number_test and update the PR accordingly.

[thulasiramk-2310]

@maddeleine I’ve moved the S2N_CLONE_SUPPORTED guard and s2n_unit_test_clone_child_process into s2n_fork_generation_number_test, and reverted s2n_safety_test to only include the initialization fix. Please let me know if this looks correct now.