1 files changed, 106 insertions, 0 deletions
diff --git a/test/test_pid.cc b/test/test_pid.cc
new file mode 100644
index 0000000..e79eb1e
--- /dev/null
+++ b/test/test_pid.cc
@@ -0,0 +1,106 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * test_pid.cc — Self-tests for PID allocator
+ *
+ * Tests: alloc, free, re-use, exhaustion guard, reserved PIDs.
+ */
+
+#include <lume/selftest.h>
+#include <lume/pid.h>
+
+void selftest_pid()
+{
+    /* Create a local PidAllocator for isolated testing */
+    PidAllocator pa;
+    pa.init();
+
+    /* ---- PID 0 is reserved (idle/swapper) ---- */
+    st_begin("pid: PID 0 is reserved");
+    {
+        /* First alloc should return 1 (PID 0 reserved for idle) */
+        int32 first = pa.alloc();
+        ST_ASSERT(first >= 1);
+    }
+    st_pass();
+
+    /* ---- Sequential allocation returns unique PIDs ---- */
+    st_begin("pid: sequential allocation returns unique PIDs");
+    {
+        PidAllocator pa2;
+        pa2.init();
+
+        int32 p1 = pa2.alloc();
+        int32 p2 = pa2.alloc();
+        int32 p3 = pa2.alloc();
+        ST_ASSERT(p1 >= 1);
+        ST_ASSERT(p2 >= 1);
+        ST_ASSERT(p3 >= 1);
+        ST_ASSERT_NE(p1, p2);
+        ST_ASSERT_NE(p2, p3);
+        ST_ASSERT_NE(p1, p3);
+    }
+    st_pass();
+
+    /* ---- Freed PID can be reused ---- */
+    st_begin("pid: freed PID can be reused");
+    {
+        PidAllocator pa3;
+        pa3.init();
+
+        /* Allocate all PIDs from 2..N */
+        constexpr int kAllocCount = 60;
+        int32 pids[kAllocCount];
+        for (int i = 0; i < kAllocCount; i++) {
+            pids[i] = pa3.alloc();
+            ST_ASSERT(pids[i] >= 1);
+        }
+
+        /* Free one in the middle */
+        int32 freed_pid = pids[kAllocCount / 2];
+        pa3.free(freed_pid);
+
+        /* Allocate again — should eventually get the freed PID */
+        bool found = false;
+        for (int i = 0; i < kAllocCount; i++) {
+            int32 p = pa3.alloc();
+            if (p == freed_pid) { found = true; break; }
+            pa3.free(p);
+        }
+        ST_ASSERT(found);
+    }
+    st_pass();
+
+    /* ---- free invalid PID is safe ---- */
+    st_begin("pid: free invalid PID is no-op");
+    {
+        PidAllocator pa4;
+        pa4.init();
+
+        /* These should not crash */
+        pa4.free(-1);
+        pa4.free(kMaxPid);
+        pa4.free(kMaxPid + 100);
+
+        /* Allocator should still work — PID 0 still reserved */
+        int32 p = pa4.alloc();
+        ST_ASSERT(p >= 1);
+    }
+    st_pass();
+
+    /* ---- Monotonic allocation before wrap ---- */
+    st_begin("pid: monotonic allocation");
+    {
+        PidAllocator pa5;
+        pa5.init();
+
+        int32 prev = pa5.alloc();
+        for (int i = 0; i < 10; i++) {
+            int32 next = pa5.alloc();
+            ST_ASSERT(next > prev);
+            prev = next;
+        }
+    }
+    st_pass();
+}