Host-side unit tests

make test runs tools/run_host_tests.py: it compiles and executes the harnesses in tests/host_*.c on the host, against the real kernel source files they include.

What runs

The runner extracts the documented gcc line from each harness header, remaps the pre-restructure paths (kernel/aead.c -> kernel/crypto/crypto_aead.c, ...), compiles with the host toolchain (ASAN where the harness asks for it) and executes it. Harnesses that need external fixtures (openssl-generated key files) compile but report SKIP-FIXTURE rather than failing.

Coverage highlights (one harness per family):

• crypto: NIST AES/SHA/HMAC vectors, RSA, X.509 parsing, AEAD
• tar / gzip / string: the lib_* primitives
• FAT structures and LFN encoding
• multiboot2 parsing (with malformed-mbi cases, ASAN)
• heap and VMM invariants

When to run it

Always. It is the fastest signal in the loop - no boot required, and it catches pure-logic regressions (checksum chains, header alignment, bounds) in seconds.

Adding a harness

1. Create tests/host_<name>.c with the standard header comment including the exact compile line (flags + include paths).
2. Count your checks and exit with the number of failures.
3. make test picks it up automatically.

The rule from CONTRIBUTING.md: never weaken a test to make it pass. If a test is wrong, fix the test and say so in the commit.