1 files changed, 102 insertions, 0 deletions
diff --git a/test/test_atomic.cc b/test/test_atomic.cc
new file mode 100644
index 0000000..9851e7b
--- /dev/null
+++ b/test/test_atomic.cc
@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * Boot Self-Test: lume::atomic<T>
+ *
+ * Tests:
+ *   1. Default construction (zero-initialized)
+ *   2. Explicit construction
+ *   3. store / load round-trip with different memory orders
+ *   4. exchange returns old value
+ *   5. fetch_add / fetch_sub arithmetic
+ *   6. compare_exchange success and failure paths
+ */
+
+#include <lume/selftest.h>
+#include <lume/atomic.h>
+
+void selftest_atomic() {
+    st_begin("atomic: default construction is zero");
+    {
+        lume::atomic<uint32> a;
+        ST_ASSERT_EQ(a.load(), 0U);
+    }
+    st_pass();
+
+    st_begin("atomic: explicit construction");
+    {
+        lume::atomic<uint64> a(42);
+        ST_ASSERT_EQ(a.load(), 42ULL);
+    }
+    st_pass();
+
+    st_begin("atomic: store/load round-trip");
+    {
+        lume::atomic<uint32> a;
+        a.store(0xDEAD, __ATOMIC_RELEASE);
+        ST_ASSERT_EQ(a.load(__ATOMIC_ACQUIRE), 0xDEADU);
+
+        a.store(0, __ATOMIC_SEQ_CST);
+        ST_ASSERT_EQ(a.load(__ATOMIC_SEQ_CST), 0U);
+    }
+    st_pass();
+
+    st_begin("atomic: exchange returns old value");
+    {
+        lume::atomic<uint32> a(10);
+        uint32 old = a.exchange(20);
+        ST_ASSERT_EQ(old, 10U);
+        ST_ASSERT_EQ(a.load(), 20U);
+    }
+    st_pass();
+
+    st_begin("atomic: fetch_add / fetch_sub");
+    {
+        lume::atomic<uint32> a(100);
+
+        uint32 old = a.fetch_add(5);
+        ST_ASSERT_EQ(old, 100U);
+        ST_ASSERT_EQ(a.load(), 105U);
+
+        old = a.fetch_sub(10);
+        ST_ASSERT_EQ(old, 105U);
+        ST_ASSERT_EQ(a.load(), 95U);
+
+        // Underflow wraps (unsigned)
+        lume::atomic<uint32> b(0);
+        old = b.fetch_sub(1);
+        ST_ASSERT_EQ(old, 0U);
+        ST_ASSERT_EQ(b.load(), 0xFFFFFFFFU);
+    }
+    st_pass();
+
+    st_begin("atomic: compare_exchange success and failure");
+    {
+        lume::atomic<uint32> a(42);
+
+        // Success path: expected matches, swap happens
+        uint32 expected = 42;
+        bool ok = a.compare_exchange(expected, 99);
+        ST_ASSERT(ok);
+        ST_ASSERT_EQ(a.load(), 99U);
+        ST_ASSERT_EQ(expected, 42U);  // expected unchanged on success
+
+        // Failure path: expected doesn't match, expected gets updated
+        expected = 0;  // wrong
+        ok = a.compare_exchange(expected, 200);
+        ST_ASSERT(!ok);
+        ST_ASSERT_EQ(a.load(), 99U);       // value unchanged
+        ST_ASSERT_EQ(expected, 99U);        // expected updated to actual value
+    }
+    st_pass();
+
+    st_begin("atomic: 64-bit fetch_add correctness");
+    {
+        lume::atomic<uint64> a(0xFFFFFFFF00000000ULL);
+        uint64 old = a.fetch_add(1);
+        ST_ASSERT_EQ(old, 0xFFFFFFFF00000000ULL);
+        ST_ASSERT_EQ(a.load(), 0xFFFFFFFF00000001ULL);
+    }
+    st_pass();
+}