diff --git a/tests/testTimeOfDay.cpp b/tests/testTimeOfDay.cpp
new file mode 100644
index 0000000..bacd664
--- /dev/null
+++ b/tests/testTimeOfDay.cpp
@@ -0,0 +1,110 @@
+#include "testHarness.h"
+#include "vf/TimeOfDay.h"
+
+using namespace vf;
+
+VF_TEST(dayFractionAndCountTrackAbsoluteTick) {
+    TimeOfDay clock;
+    CHECK_EQ(clock.dayCount(), static_cast<WorldTick>(0));
+    CHECK_NEAR(clock.dayFraction(), 0.0, 1e-9);
+
+    clock.setTick(12000);
+    CHECK_NEAR(clock.dayFraction(), 0.5, 1e-9);
+    CHECK_EQ(clock.timeOfDayTicks(), static_cast<WorldTick>(12000));
+
+    clock.setTick(24000 * 3 + 6000);
+    CHECK_EQ(clock.dayCount(), static_cast<WorldTick>(3));
+    CHECK_NEAR(clock.dayFraction(), 0.25, 1e-9);
+}
+
+VF_TEST(phasesMapToClockPositions) {
+    TimeOfDay clock;
+    clock.setTick(0);
+    CHECK(clock.phase() == DayPhase::Night);
+    clock.setTick(6000);
+    CHECK(clock.phase() == DayPhase::Dawn);
+    clock.setTick(12000);
+    CHECK(clock.phase() == DayPhase::Day);
+    clock.setTick(18000);
+    CHECK(clock.phase() == DayPhase::Dusk);
+    clock.setTick(21600);
+    CHECK(clock.phase() == DayPhase::Night);
+}
+
+VF_TEST(skyLightPeaksAtNoonAndBottomsAtMidnight) {
+    TimeOfDay clock;
+    clock.setTick(12000);
+    CHECK_EQ(clock.skyLightLevel(), 15);
+    clock.setTick(0);
+    CHECK_EQ(clock.skyLightLevel(), 4);
+
+    clock.setTick(6000);
+    int dawnLevel = clock.skyLightLevel();
+    CHECK(dawnLevel > 4);
+    CHECK(dawnLevel < 15);
+}
+
+VF_TEST(skyLightRisesMonotonicallyThroughDawn) {
+    TimeOfDay clock;
+    int previous = -1;
+    for (WorldTick t = 4800; t <= 7200; t += 200) {
+        clock.setTick(t);
+        int level = clock.skyLightLevel();
+        CHECK(level >= previous);
+        previous = level;
+    }
+    clock.setTick(4800);
+    CHECK_EQ(clock.skyLightLevel(), 4);
+    clock.setTick(7200);
+    CHECK_EQ(clock.skyLightLevel(), 15);
+}
+
+VF_TEST(sunHeightPositiveByDayNegativeByNight) {
+    TimeOfDay clock;
+    clock.setTick(12000);
+    CHECK(clock.sunHeight() > 0.99);
+    clock.setTick(0);
+    CHECK(clock.sunHeight() < -0.99);
+}
+
+VF_TEST(moonPhaseAdvancesOncePerDayAndWraps) {
+    TimeOfDay clock;
+    clock.setTick(0);
+    CHECK_EQ(clock.moonPhase(), 0);
+    clock.setTick(24000);
+    CHECK_EQ(clock.moonPhase(), 1);
+    clock.setTick(24000 * 7);
+    CHECK_EQ(clock.moonPhase(), 7);
+    clock.setTick(24000 * 8);
+    CHECK_EQ(clock.moonPhase(), 0);
+}
+
+VF_TEST(sunriseCrossingDetectedExactlyOnce) {
+    TimeOfDay clock(0);
+    clock.advance(5999);
+    CHECK(!clock.crossedSunrise());
+    clock.advance(1);
+    CHECK(clock.crossedSunrise());
+    CHECK(!clock.crossedSunset());
+
+    clock.advance(1);
+    CHECK(!clock.crossedSunrise());
+}
+
+VF_TEST(sunsetCrossingDetectedAcrossInterval) {
+    TimeOfDay clock(6000);
+    clock.advance(12000);
+    CHECK(clock.crossedSunset());
+    CHECK(!clock.crossedSunrise());
+    CHECK_EQ(clock.absoluteTick(), static_cast<WorldTick>(18000));
+}
+
+VF_TEST(advanceAccumulatesDaysDeterministically) {
+    TimeOfDay a(0);
+    for (int i = 0; i < 240; ++i) a.advance(100);
+    TimeOfDay b(0);
+    b.advance(24000);
+    CHECK_EQ(a.absoluteTick(), b.absoluteTick());
+    CHECK_EQ(a.dayCount(), b.dayCount());
+    CHECK_NEAR(a.dayFraction(), b.dayFraction(), 1e-9);
+}