diff --git a/tests/testStructures.cpp b/tests/testStructures.cpp
new file mode 100644
index 0000000..58e593f
--- /dev/null
+++ b/tests/testStructures.cpp
@@ -0,0 +1,123 @@
+#include "testHarness.h"
+#include "vf/Structures.h"
+#include "vf/WorldGen.h"
+
+using namespace vf;
+
+namespace {
+
+bool sameEdits(const std::vector<StructureEdit>& a, const std::vector<StructureEdit>& b) {
+    if (a.size() != b.size()) return false;
+    for (std::size_t i = 0; i < a.size(); ++i) {
+        if (!(a[i].offset == b[i].offset) || a[i].block != b[i].block) return false;
+    }
+    return true;
+}
+
+std::size_t countBlock(const World& world, Block target) {
+    std::size_t total = 0;
+    for (const auto& entry : world.allChunks())
+        for (Block b : entry.second->raw())
+            if (b == target) ++total;
+    return total;
+}
+
+bool worldsEqual(const World& a, const World& b) {
+    if (a.chunkCount() != b.chunkCount()) return false;
+    for (const auto& entry : a.allChunks()) {
+        const Chunk* other = b.chunkAt(entry.first);
+        if (!other) return false;
+        if (entry.second->raw() != other->raw()) return false;
+    }
+    return true;
+}
+
+} // namespace
+
+VF_TEST(structureBuildIsDeterministicPerSeed) {
+    std::vector<StructureEdit> oakA = buildStructure(StructureKind::OakTree, 12345u);
+    std::vector<StructureEdit> oakB = buildStructure(StructureKind::OakTree, 12345u);
+    CHECK(sameEdits(oakA, oakB));   // same seed, same tree
+
+    std::vector<StructureEdit> oakC = buildStructure(StructureKind::OakTree, 999u);
+    CHECK(!sameEdits(oakA, oakC));  // different seed, different tree
+    CHECK(!oakA.empty());
+}
+
+VF_TEST(structureHutHasLanternFloorAndDoor) {
+    std::vector<StructureEdit> hut = buildStructure(StructureKind::Hut, 7u);
+    bool lantern = false, floorCentre = false, doorOpen = true;
+    for (const StructureEdit& e : hut) {
+        if (e.block == Block::Glowstone) lantern = true;
+        if (e.offset == Vec3i(0, 0, 0) && e.block == Block::Wood) floorCentre = true;
+        if (e.offset == Vec3i(0, 1, -2)) doorOpen = false;   // doorway cell must stay empty
+    }
+    CHECK(lantern);
+    CHECK(floorCentre);
+    CHECK(doorOpen);
+}
+
+VF_TEST(structureStampWritesBlocks) {
+    World world;
+    std::vector<StructureEdit> oak = buildStructure(StructureKind::OakTree, 42u);
+    stampStructure(world, {100, 40, 100}, oak, 128);
+    CHECK(world.blockAt(100, 40, 100) == Block::Wood);   // trunk base
+    CHECK(countBlock(world, Block::Leaves) > 0);         // canopy present
+}
+
+VF_TEST(structureLeavesDoNotOverwriteSolids) {
+    World world;
+    world.setBlock(100, 41, 100, Block::Stone);   // pre-existing solid where a leaf would go
+    std::vector<StructureEdit> oak = buildStructure(StructureKind::OakTree, 42u);
+    stampStructure(world, {100, 40, 100}, oak, 128);
+    CHECK(world.blockAt(100, 41, 100) == Block::Wood || world.blockAt(100, 41, 100) == Block::Stone);
+    // trunk (wood) may overwrite, but no leaf replaced the stone
+}
+
+VF_TEST(worldGenWithStructuresIsDeterministic) {
+    WorldGenParams params;
+    params.structures = true;
+    WorldGen genA(params), genB(params);
+    World a, b;
+    for (int cx = 0; cx < 5; ++cx)
+        for (int cz = 0; cz < 5; ++cz) {
+            genA.generateColumn(a, cx, cz);
+            genB.generateColumn(b, cx, cz);
+        }
+    CHECK(worldsEqual(a, b));   // same seed -> identical structures and terrain
+}
+
+VF_TEST(worldGenDifferentSeedDiffersWithStructures) {
+    WorldGenParams pa;
+    pa.seed = 1337u;
+    WorldGenParams pb;
+    pb.seed = 2024u;
+    WorldGen genA(pa), genB(pb);
+    World a, b;
+    for (int cx = 0; cx < 5; ++cx)
+        for (int cz = 0; cz < 5; ++cz) {
+            genA.generateColumn(a, cx, cz);
+            genB.generateColumn(b, cx, cz);
+        }
+    CHECK(!worldsEqual(a, b));
+}
+
+VF_TEST(worldGenStampsHutsWhenEnabled) {
+    WorldGenParams on;
+    on.structures = true;
+    WorldGen gen(on);
+    World world;
+    for (int cx = 0; cx < 16; ++cx)
+        for (int cz = 0; cz < 16; ++cz)
+            gen.generateColumn(world, cx, cz);
+    CHECK(countBlock(world, Block::Glowstone) > 0);   // lantern proves a hut was stamped
+
+    WorldGenParams off;
+    off.structures = false;
+    WorldGen bare(off);
+    World plain;
+    for (int cx = 0; cx < 16; ++cx)
+        for (int cz = 0; cz < 16; ++cz)
+            bare.generateColumn(plain, cx, cz);
+    CHECK_EQ(countBlock(plain, Block::Glowstone), static_cast<std::size_t>(0));
+}