diff --git a/tests/domain/runtime-npc-presence.test.ts b/tests/domain/runtime-npc-presence.test.ts
new file mode 100644
index 00000000..0e9e56df
--- /dev/null
+++ b/tests/domain/runtime-npc-presence.test.ts
@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  createNpcAlwaysPresence,
+  createNpcTimeWindowPresence
+} from "../../src/entities/entity-instances";
+import {
+  hasNpcPresenceActivityChanged,
+  resolveNpcPresenceActive
+} from "../../src/runtime-three/runtime-npc-presence";
+
+describe("runtime NPC presence", () => {
+  it("keeps always-authored NPC presence active at any time of day", () => {
+    const presence = createNpcAlwaysPresence();
+
+    expect(resolveNpcPresenceActive(presence, 2)).toBe(true);
+    expect(resolveNpcPresenceActive(presence, 14.5)).toBe(true);
+    expect(
+      hasNpcPresenceActivityChanged(presence, 6, 18)
+    ).toBe(false);
+  });
+
+  it("resolves time-windowed NPC presence across midnight and detects window boundaries", () => {
+    const presence = createNpcTimeWindowPresence({
+      startHour: 22,
+      endHour: 2
+    });
+
+    expect(resolveNpcPresenceActive(presence, 21.5)).toBe(false);
+    expect(resolveNpcPresenceActive(presence, 23.5)).toBe(true);
+    expect(resolveNpcPresenceActive(presence, 1.5)).toBe(true);
+    expect(resolveNpcPresenceActive(presence, 3)).toBe(false);
+
+    expect(hasNpcPresenceActivityChanged(presence, 21.5, 23)).toBe(true);
+    expect(hasNpcPresenceActivityChanged(presence, 23, 1)).toBe(false);
+    expect(hasNpcPresenceActivityChanged(presence, 1.5, 2.5)).toBe(true);
+  });
+});