diff --git a/tests/testEntity.cpp b/tests/testEntity.cpp
new file mode 100644
index 0000000..a60dee8
--- /dev/null
+++ b/tests/testEntity.cpp
@@ -0,0 +1,123 @@
+#include "testHarness.h"
+#include "vf/Entity.h"
+
+using namespace vf;
+
+namespace {
+
+World floorWorld(int x0 = -4, int z0 = -4, int x1 = 24, int z1 = 24) {
+    World world;
+    for (int x = x0; x <= x1; ++x)
+        for (int z = z0; z <= z1; ++z)
+            world.setBlock(x, 0, z, Block::Stone);
+    return world;
+}
+
+} // namespace
+
+VF_TEST(mobFallsAndLandsOnFloor) {
+    World world = floorWorld();
+    Mob mob;
+    mob.position = {5.0f, 6.0f, 5.0f};
+    MobConfig config;
+
+    for (int i = 0; i < 240; ++i) stepMob(world, mob, {0, 0, 0}, config, 1.0f / 60.0f);
+
+    CHECK(mob.onGround);
+    CHECK_NEAR(mob.position.y, 1.0f, 0.02f);
+    CHECK(!boxOverlapsSolid(world, mobBox(mob)));
+}
+
+VF_TEST(mobStopsAtWall) {
+    World world = floorWorld();
+    for (int y = 1; y <= 3; ++y)
+        for (int z = -4; z <= 24; ++z)
+            world.setBlock(10, y, z, Block::Stone);
+
+    Mob mob;
+    mob.position = {5.0f, 1.0f, 5.0f};
+    MobConfig config;
+
+    for (int i = 0; i < 300; ++i) stepMob(world, mob, {1.0f, 0.0f, 0.0f}, config, 1.0f / 60.0f);
+
+    CHECK(mob.position.x + mob.width * 0.5f <= 10.0f + 1e-3f);
+    CHECK(!boxOverlapsSolid(world, mobBox(mob)));
+}
+
+VF_TEST(mobBrainWandersWhenTargetFar) {
+    World world = floorWorld();
+    Mob mob;
+    mob.position = {5.0f, 1.0f, 5.0f};
+    MobConfig config;
+    Vec3 target{80.0f, 1.0f, 80.0f};   // way past chaseRadius
+
+    Vec3 wish = updateMobBrain(world, mob, target, config);
+    CHECK(mob.state == MobState::Wander);
+    CHECK(length(wish) > 0.5f);   // still produces a heading
+}
+
+VF_TEST(mobBrainChasesReachableTarget) {
+    World world = floorWorld();
+    Mob mob;
+    mob.position = {5.0f, 1.0f, 5.0f};
+    MobConfig config;
+    Vec3 target{9.0f, 1.0f, 5.0f};   // within chaseRadius, open ground
+
+    Vec3 wish = updateMobBrain(world, mob, target, config);
+    CHECK(mob.state == MobState::Chase);
+    CHECK(wish.x > 0.5f);   // heads toward +x target
+    CHECK(wish.x > std::fabs(wish.z));   // +x is the dominant component
+}
+
+VF_TEST(mobBrainHysteresisKeepsChaseInBand) {
+    World world = floorWorld();
+    Mob mob;
+    mob.position = {5.0f, 1.0f, 5.0f};
+    mob.state = MobState::Chase;
+    MobConfig config;   // chase 12, lose 16
+    Vec3 inBand{5.0f + 14.0f, 1.0f, 5.0f};   // between chase and lose
+
+    updateMobBrain(world, mob, inBand, config);
+    CHECK(mob.state == MobState::Chase);   // stays chasing in the band
+
+    Vec3 farOut{5.0f + 20.0f, 1.0f, 5.0f};
+    updateMobBrain(world, mob, farOut, config);
+    CHECK(mob.state == MobState::Wander);   // drops chase past loseRadius
+}
+
+VF_TEST(mobBrainWandersWhenTargetUnreachable) {
+    World world = floorWorld();
+    // seal a target cell at {9,1,5}
+    for (int y = 1; y <= 2; ++y) {
+        world.setBlock(8, y, 5, Block::Stone);
+        world.setBlock(10, y, 5, Block::Stone);
+        world.setBlock(9, y, 4, Block::Stone);
+        world.setBlock(9, y, 6, Block::Stone);
+    }
+    Mob mob;
+    mob.position = {5.0f, 1.0f, 5.0f};
+    MobConfig config;
+    Vec3 target{9.0f, 1.0f, 5.0f};   // in range but sealed off
+
+    updateMobBrain(world, mob, target, config);
+    CHECK(mob.state == MobState::Wander);
+}
+
+VF_TEST(mobChaseClosesDistanceOverTime) {
+    World world = floorWorld(-4, -4, 30, 30);
+    Mob mob;
+    mob.position = {2.5f, 1.0f, 2.5f};
+    MobConfig config;
+    config.chaseRadius = 40.0f;
+    config.loseRadius = 50.0f;
+    Vec3 target{18.5f, 1.0f, 2.5f};
+
+    float startDist = mob.position.x;
+    for (int i = 0; i < 500; ++i) {
+        Vec3 wish = updateMobBrain(world, mob, target, config);
+        stepMob(world, mob, wish, config, 1.0f / 60.0f);
+    }
+    CHECK(mob.state == MobState::Chase);
+    CHECK(mob.position.x > startDist + 10.0f);        // advanced toward the target
+    CHECK(std::fabs(mob.position.x - target.x) < 1.5f);   // arrived near it
+}