diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 3df09f5..6e5d63c 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -22,7 +22,8 @@ jobs:
         run: |
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends \
-            build-essential clang make linux-libc-dev
+            build-essential clang make linux-libc-dev \
+            libglib2.0-dev pkg-config
 
       - name: show compiler
         run: ${{ matrix.cc }} --version
@@ -54,6 +55,18 @@ jobs:
       - name: sanity — --detect-rules sigma
         run: ./skeletonkey --detect-rules --format=sigma | head -50
 
+      - name: tests — detect() unit suite
+        env:
+          CC: ${{ matrix.cc }}
+        run: |
+          # Run as a non-root user so modules' "already root" gates do
+          # not short-circuit before the synthetic host-fingerprint
+          # checks fire. The test binary itself is platform-agnostic;
+          # the assertions are #ifdef __linux__ guarded.
+          sudo useradd -m -s /bin/bash skeletonkeyci 2>/dev/null || true
+          sudo chown -R skeletonkeyci .
+          sudo -u skeletonkeyci make test
+
   # Static build job: ensures the project links cleanly when -static is
   # requested. Useful for deployment to minimal containers / fleet scans
   # where shared-libc availability isn't guaranteed.
@@ -66,7 +79,8 @@ jobs:
         run: |
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends \
-            build-essential make linux-libc-dev libc6-dev
+            build-essential make linux-libc-dev libc6-dev \
+            libglib2.0-dev pkg-config
       - name: make static
         # Glibc static linking pulls in NSS at runtime which breaks
         # getpwnam; the legacy DIRTYFAIL Makefile noted this. For now,
diff --git a/Makefile b/Makefile
index aaa2451..bf39759 100644
--- a/Makefile
+++ b/Makefile
@@ -177,15 +177,40 @@ $(P2TR_OBJS): CFLAGS += $(P2TR_CFLAGS)
 # Top-level dispatcher
 TOP_OBJ  := $(BUILD)/skeletonkey.o
 
-ALL_OBJS := $(TOP_OBJ) $(CORE_OBJS) $(CFF_OBJS) $(DP_OBJS) $(EB_OBJS) $(PK_OBJS) $(NFT_OBJS) $(OVL_OBJS) $(CR4_OBJS) $(DCOW_OBJS) $(PTM_OBJS) $(NXC_OBJS) $(AFP_OBJS) $(FUL_OBJS) $(STR_OBJS) $(AFP2_OBJS) $(CRA_OBJS) $(OSU_OBJS) $(NSU_OBJS) $(AUG_OBJS) $(NFD_OBJS) $(NPL_OBJS) $(SAM_OBJS) $(SEQ_OBJS) $(SUE_OBJS) $(VMW_OBJS) $(DDC_OBJS) $(FGN_OBJS) $(P2TR_OBJS)
+# All module objects in one var so both the main binary and the test
+# binary can re-use the list without duplicating the long enumeration.
+MODULE_OBJS := $(CFF_OBJS) $(DP_OBJS) $(EB_OBJS) $(PK_OBJS) $(NFT_OBJS) \
+               $(OVL_OBJS) $(CR4_OBJS) $(DCOW_OBJS) $(PTM_OBJS) $(NXC_OBJS) \
+               $(AFP_OBJS) $(FUL_OBJS) $(STR_OBJS) $(AFP2_OBJS) $(CRA_OBJS) \
+               $(OSU_OBJS) $(NSU_OBJS) $(AUG_OBJS) $(NFD_OBJS) $(NPL_OBJS) \
+               $(SAM_OBJS) $(SEQ_OBJS) $(SUE_OBJS) $(VMW_OBJS) \
+               $(DDC_OBJS) $(FGN_OBJS) $(P2TR_OBJS)
 
-.PHONY: all clean debug static help
+ALL_OBJS := $(TOP_OBJ) $(CORE_OBJS) $(MODULE_OBJS)
+
+# Tests — `make test` builds and runs the detect() unit-test harness.
+# Links against the same module objects as the main binary minus the
+# top-level dispatcher (which provides main(); the test has its own).
+TEST_DIR  := tests
+TEST_SRCS := $(TEST_DIR)/test_detect.c
+TEST_OBJS := $(patsubst %.c,$(BUILD)/%.o,$(TEST_SRCS))
+TEST_BIN  := skeletonkey-test
+TEST_ALL_OBJS := $(TEST_OBJS) $(CORE_OBJS) $(MODULE_OBJS)
+
+.PHONY: all clean debug static help test
 
 all: $(BIN)
 
 $(BIN): $(ALL_OBJS)
 	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ -lpthread $(P2TR_LIBS)
 
+$(TEST_BIN): $(TEST_ALL_OBJS)
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ -lpthread $(P2TR_LIBS)
+
+test: $(TEST_BIN)
+	@echo "[*] running test suite ($(TEST_BIN))"
+	./$(TEST_BIN)
+
 # Generic compile: any .c → corresponding .o under build/
 $(BUILD)/%.o: %.c
 	@mkdir -p $(dir $@)
@@ -198,13 +223,14 @@ static: LDFLAGS += -static
 static: clean $(BIN)
 
 clean:
-	rm -rf $(BUILD) $(BIN)
+	rm -rf $(BUILD) $(BIN) $(TEST_BIN)
 
 help:
 	@echo "Targets:"
 	@echo "  make           build optimized skeletonkey binary"
 	@echo "  make debug     build with -O0 -g3"
 	@echo "  make static    build a fully static binary"
+	@echo "  make test      build + run the detect() unit test suite"
 	@echo "  make clean     remove build artifacts"
 	@echo ""
 	@echo "Per-module (legacy) — not built by default:"
diff --git a/modules/pack2theroot_cve_2026_41651/skeletonkey_modules.c b/modules/pack2theroot_cve_2026_41651/skeletonkey_modules.c
index 07a11a8..2ee38b2 100644
--- a/modules/pack2theroot_cve_2026_41651/skeletonkey_modules.c
+++ b/modules/pack2theroot_cve_2026_41651/skeletonkey_modules.c
@@ -305,7 +305,12 @@ static skeletonkey_result_t p2tr_detect(const struct skeletonkey_ctx *ctx)
 {
 	p2tr_verbose = !ctx->json;
 
-	if (geteuid() == 0) {
+	/* "Already root" check — consult ctx->host first so unit tests
+	 * can construct a non-root fingerprint regardless of the test
+	 * process's real euid. Production main() populates host->is_root
+	 * from geteuid() at startup, so behaviour is unchanged. */
+	bool is_root = ctx->host ? ctx->host->is_root : (geteuid() == 0);
+	if (is_root) {
 		if (!ctx->json)
 			fprintf(stderr, "[i] pack2theroot: already root — nothing to do\n");
 		return SKELETONKEY_OK;
diff --git a/skeletonkey-test b/skeletonkey-test
new file mode 100755
index 0000000..ad8c83b
Binary files /dev/null and b/skeletonkey-test differ
diff --git a/tests/test_detect.c b/tests/test_detect.c
new file mode 100644
index 0000000..fd1c1e1
--- /dev/null
+++ b/tests/test_detect.c
@@ -0,0 +1,191 @@
+/*
+ * tests/test_detect.c — detect() unit tests
+ *
+ * Each test builds a synthetic struct skeletonkey_host fingerprint
+ * (vulnerable / patched / specific-gate-closed) and asserts each
+ * module's detect() returns the expected verdict. Catches regressions
+ * in the host-fingerprint-consuming logic across the corpus.
+ *
+ * Coverage today is the four modules that already consume ctx->host:
+ *   - dirtydecrypt   (CVE-2026-31635)
+ *   - fragnesia      (CVE-2026-46300)
+ *   - pack2theroot   (CVE-2026-41651)
+ *   - overlayfs      (CVE-2021-3493)
+ * Coverage grows automatically as more modules migrate to ctx->host
+ * (see ROADMAP "core/host" follow-up).
+ *
+ * Why only Linux: every module's real detect() lives inside
+ * `#ifdef __linux__`; on non-Linux the stubs unconditionally return
+ * PRECOND_FAIL so the tests are tautologies. The harness compiles
+ * cross-platform but skips the assertions on non-Linux to keep the
+ * macOS dev build green while still preventing bit-rot of the test
+ * infrastructure.
+ */
+
+#include "../core/module.h"
+#include "../core/host.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+extern const struct skeletonkey_module dirtydecrypt_module;
+extern const struct skeletonkey_module fragnesia_module;
+extern const struct skeletonkey_module pack2theroot_module;
+extern const struct skeletonkey_module overlayfs_module;
+
+static int g_pass = 0;
+static int g_fail = 0;
+
+static const char *result_str(skeletonkey_result_t r)
+{
+	switch (r) {
+	case SKELETONKEY_OK:           return "OK";
+	case SKELETONKEY_TEST_ERROR:   return "TEST_ERROR";
+	case SKELETONKEY_VULNERABLE:   return "VULNERABLE";
+	case SKELETONKEY_EXPLOIT_FAIL: return "EXPLOIT_FAIL";
+	case SKELETONKEY_PRECOND_FAIL: return "PRECOND_FAIL";
+	case SKELETONKEY_EXPLOIT_OK:   return "EXPLOIT_OK";
+	}
+	return "???";
+}
+
+#ifdef __linux__
+/* Suppress per-module banner chatter so the test output stays tidy.
+ * Modules respect ctx->json to mean "structured output mode; no banners"
+ * — see each module's `if (!ctx->json) fprintf(...)` pattern. */
+static void run_one(const char *test_name,
+		    const struct skeletonkey_module *m,
+		    const struct skeletonkey_host *h,
+		    skeletonkey_result_t want)
+{
+	struct skeletonkey_ctx ctx = {0};
+	ctx.host = h;
+	ctx.json = true;        /* silence per-module log lines */
+
+	skeletonkey_result_t got = m->detect(&ctx);
+	if (got == want) {
+		printf("[+] PASS  %-40s  %s → %s\n",
+		       test_name, m->name, result_str(got));
+		g_pass++;
+	} else {
+		fprintf(stderr,
+			"[-] FAIL  %-40s  %s: want %s, got %s\n",
+			test_name, m->name,
+			result_str(want), result_str(got));
+		g_fail++;
+	}
+}
+
+/* ── fingerprints ────────────────────────────────────────────────── */
+
+/* Linux 6.12.76 (Debian 13), no userns, no D-Bus, not Ubuntu — a
+ * deliberately neutered host that lets the host-fingerprint-only
+ * gates fire without falling into deeper module logic. */
+static const struct skeletonkey_host h_pre7_no_userns_no_dbus = {
+	.kernel  = { .major = 6, .minor = 12, .patch = 76,
+		     .release = "6.12.76-test" },
+	.arch    = "x86_64",
+	.nodename = "test",
+	.distro_id          = "debian",
+	.distro_version_id  = "13",
+	.distro_pretty      = "Debian GNU/Linux 13",
+	.is_linux           = true,
+	.is_debian_family   = true,
+	.unprivileged_userns_allowed = false,
+	.has_dbus_system    = false,
+	.has_systemd        = true,
+};
+
+/* Fedora 43, no Debian family, userns allowed. */
+static const struct skeletonkey_host h_fedora_no_debian = {
+	.kernel  = { .major = 6, .minor = 14, .patch = 0,
+		     .release = "6.14.0-fedora" },
+	.arch    = "x86_64",
+	.nodename = "test",
+	.distro_id          = "fedora",
+	.distro_version_id  = "43",
+	.distro_pretty      = "Fedora 43",
+	.is_linux           = true,
+	.is_rpm_family      = true,
+	.is_debian_family   = false,
+	.unprivileged_userns_allowed = true,
+	.has_dbus_system    = true,
+	.has_systemd        = true,
+};
+
+/* Ubuntu 24.04, userns allowed, D-Bus running, Debian family
+ * (because Ubuntu has /etc/debian_version). Used as the "fragnesia
+ * preconditions OK" baseline — fragnesia should NOT short-circuit
+ * on userns/userspace gates here. */
+static const struct skeletonkey_host h_ubuntu_24_userns_ok = {
+	.kernel  = { .major = 6, .minor = 8, .patch = 0,
+		     .release = "6.8.0-ubuntu" },
+	.arch    = "x86_64",
+	.nodename = "test",
+	.distro_id          = "ubuntu",
+	.distro_version_id  = "24.04",
+	.distro_pretty      = "Ubuntu 24.04 LTS",
+	.is_linux           = true,
+	.is_debian_family   = true,
+	.unprivileged_userns_allowed = true,
+	.has_dbus_system    = true,
+	.has_systemd        = true,
+};
+#endif /* __linux__ */
+
+/* ── tests ───────────────────────────────────────────────────────── */
+
+static void run_all(void)
+{
+#ifdef __linux__
+	/* dirtydecrypt: kernel.major < 7 → predates the bug → OK */
+	run_one("dirtydecrypt: kernel 6.12 predates 7.0 → OK",
+		&dirtydecrypt_module, &h_pre7_no_userns_no_dbus,
+		SKELETONKEY_OK);
+
+	run_one("dirtydecrypt: kernel 6.14 (fedora) still predates → OK",
+		&dirtydecrypt_module, &h_fedora_no_debian,
+		SKELETONKEY_OK);
+
+	run_one("dirtydecrypt: kernel 6.8 (ubuntu) still predates → OK",
+		&dirtydecrypt_module, &h_ubuntu_24_userns_ok,
+		SKELETONKEY_OK);
+
+	/* fragnesia: userns disabled → XFRM gate closed → PRECOND_FAIL */
+	run_one("fragnesia: userns_allowed=false → PRECOND_FAIL",
+		&fragnesia_module, &h_pre7_no_userns_no_dbus,
+		SKELETONKEY_PRECOND_FAIL);
+
+	/* pack2theroot: not Debian family → PRECOND_FAIL */
+	run_one("pack2theroot: is_debian_family=false → PRECOND_FAIL",
+		&pack2theroot_module, &h_fedora_no_debian,
+		SKELETONKEY_PRECOND_FAIL);
+
+	/* pack2theroot: Debian family but no D-Bus socket → PRECOND_FAIL */
+	run_one("pack2theroot: has_dbus_system=false → PRECOND_FAIL",
+		&pack2theroot_module, &h_pre7_no_userns_no_dbus,
+		SKELETONKEY_PRECOND_FAIL);
+
+	/* overlayfs: distro != ubuntu → bug is Ubuntu-specific → OK */
+	run_one("overlayfs: distro=debian → not Ubuntu → OK",
+		&overlayfs_module, &h_pre7_no_userns_no_dbus,
+		SKELETONKEY_OK);
+
+	run_one("overlayfs: distro=fedora → not Ubuntu → OK",
+		&overlayfs_module, &h_fedora_no_debian,
+		SKELETONKEY_OK);
+#else
+	fprintf(stderr, "[i] non-Linux platform: detect() bodies are stubbed; "
+			"tests skipped (would tautologically pass).\n");
+#endif
+}
+
+int main(void)
+{
+	fprintf(stderr, "=== SKELETONKEY detect() unit tests ===\n\n");
+	run_all();
+	fprintf(stderr, "\n=== RESULTS: %d passed, %d failed ===\n",
+		g_pass, g_fail);
+	return g_fail ? 1 : 0;
+}