diff --git a/tests/testContainer.cpp b/tests/testContainer.cpp
new file mode 100644
index 0000000..37eecf1
--- /dev/null
+++ b/tests/testContainer.cpp
@@ -0,0 +1,123 @@
+#include "testHarness.h"
+#include "vf/Container.h"
+
+using namespace vf;
+
+VF_TEST(insertMergesIntoMatchingStackThenSpillsToNewSlot) {
+    Container box(3);
+    CHECK_EQ(box.insert(ItemId::Stone, 40), 0);
+    CHECK_EQ(box.insert(ItemId::Stone, 40), 0);
+    CHECK_EQ(box.usedSlots(), 2);
+    CHECK_EQ(box.totalItems(), 80);
+    CHECK_EQ(box.slot(0).count, 64);
+    CHECK_EQ(box.slot(1).count, 16);
+}
+
+VF_TEST(insertReturnsLeftoverWhenContainerCannotHoldAll) {
+    Container box(1);
+    int leftover = box.insert(ItemId::Dirt, 100);
+    CHECK_EQ(leftover, 36);
+    CHECK_EQ(box.slot(0).count, 64);
+    CHECK(box.isFull());
+}
+
+VF_TEST(isEmptyAndIsFullReflectContents) {
+    Container box(2);
+    CHECK(box.isEmpty());
+    CHECK(!box.isFull());
+    box.insert(ItemId::Stone, 64);
+    CHECK(!box.isEmpty());
+    CHECK(!box.isFull());
+    box.insert(ItemId::Stone, 64);
+    CHECK(box.isFull());
+}
+
+VF_TEST(extractPullsMatchingItemsAcrossSlots) {
+    Container box(4);
+    box.insert(ItemId::Cobblestone, 64);
+    box.insert(ItemId::Cobblestone, 20);
+    ItemSlot pulled = box.extract(ItemId::Cobblestone, 70);
+    CHECK_EQ(static_cast<int>(pulled.item), static_cast<int>(ItemId::Cobblestone));
+    CHECK_EQ(pulled.count, 70);
+    CHECK_EQ(box.totalItems(), 14);
+}
+
+VF_TEST(extractReturnsEmptyWhenItemAbsent) {
+    Container box(2);
+    box.insert(ItemId::Stone, 10);
+    ItemSlot pulled = box.extract(ItemId::Dirt, 5);
+    CHECK(pulled.empty());
+    CHECK_EQ(box.totalItems(), 10);
+}
+
+VF_TEST(transferMovesRequestedAmountAndStopsAtDestinationCapacity) {
+    Container src(2);
+    Container dst(1);
+    src.insert(ItemId::Stone, 50);
+    int moved = src.transferTo(dst, 30);
+    CHECK_EQ(moved, 30);
+    CHECK_EQ(dst.totalItems(), 30);
+    CHECK_EQ(src.totalItems(), 20);
+}
+
+VF_TEST(transferBlockedWhenDestinationFull) {
+    Container src(1);
+    Container dst(1);
+    dst.insert(ItemId::Stone, 64);
+    src.insert(ItemId::Stone, 10);
+    int moved = src.transferTo(dst, 5);
+    CHECK_EQ(moved, 0);
+    CHECK_EQ(dst.totalItems(), 64);
+    CHECK_EQ(src.totalItems(), 10);
+}
+
+VF_TEST(comparatorSignalScalesWithFill) {
+    Container empty(1);
+    CHECK_EQ(empty.comparatorSignal(), 0);
+
+    Container half(1);
+    half.insert(ItemId::Stone, 32);
+    CHECK_EQ(half.comparatorSignal(), 8);
+
+    Container full(1);
+    full.insert(ItemId::Stone, 64);
+    CHECK_EQ(full.comparatorSignal(), 15);
+}
+
+VF_TEST(comparatorSignalAveragesAcrossSlots) {
+    Container box(4);
+    box.insert(ItemId::Stone, 64);
+    CHECK(box.comparatorSignal() > 0);
+    CHECK(box.comparatorSignal() < 8);
+}
+
+VF_TEST(toolsDoNotStackAndKeepDurability) {
+    Container box(4);
+    ItemSlot pick = makeToolStack(ItemId::WoodPickaxe);
+    ItemSlot copyA = pick;
+    ItemSlot copyB = pick;
+    box.insert(copyA);
+    box.insert(copyB);
+    CHECK_EQ(box.usedSlots(), 2);
+    CHECK(box.slot(0).durability > 0);
+}
+
+VF_TEST(extractSlotSplitsExactCount) {
+    Container box(2);
+    box.insert(ItemId::Sand, 40);
+    ItemSlot piece = box.extractSlot(0, 15);
+    CHECK_EQ(piece.count, 15);
+    CHECK_EQ(box.slot(0).count, 25);
+}
+
+VF_TEST(storeCreatesAndAddressesContainersByCell) {
+    ContainerStore store;
+    CHECK(!store.has({2, 3, 4}));
+    Container& box = store.ensure({2, 3, 4}, 5);
+    box.insert(ItemId::Stone, 5);
+    CHECK(store.has({2, 3, 4}));
+    CHECK_EQ(store.at({2, 3, 4})->totalItems(), 5);
+    CHECK(store.at({9, 9, 9}) == nullptr);
+    store.remove({2, 3, 4});
+    CHECK(!store.has({2, 3, 4}));
+}