diff --git a/market/orderbook/orderbook_test.go b/market/orderbook/orderbook_test.go
new file mode 100644
index 00000000..94880af7
--- /dev/null
+++ b/market/orderbook/orderbook_test.go
@@ -0,0 +1,58 @@
+// orderbook_test.go
+
+package orderbook
+
+import (
+	"testing"
+)
+
+func TestCancelBid(t *testing.T) {
+	ob := NewOrderBook()
+	orderID := ob.AddBid(100, 1)
+	ob.CancelOrder(orderID)
+
+	if _, exists := ob.bids[orderID]; exists {
+		t.Fatalf("expected bid to be removed, but it still exists")
+	}
+}
+
+func TestCancelAsk(t *testing.T) {
+	ob := NewOrderBook()
+	orderID := ob.AddAsk(100, 1)
+	ob.CancelOrder(orderID)
+
+	if _, exists := ob.asks[orderID]; exists {
+		t.Fatalf("expected ask to be removed, but it still exists")
+	}
+}
+
+func TestCancelUnknownOrder(t *testing.T) {
+	ob := NewOrderBook()
+	err := ob.CancelOrder("unknownID")
+
+	if err != ErrOrderNotFound {
+		t.Fatalf("expected ErrOrderNotFound, got %v", err)
+	}
+}
+
+func TestClosedBookRejectsOperations(t *testing.T) {
+	ob := NewOrderBook()
+	ob.Close()
+	err := ob.AddBid(100, 1)
+
+	if err != ErrBookClosed {
+		t.Fatalf("expected ErrBookClosed, got %v", err)
+	}
+}
+
+func TestSnapshotImmutability(t *testing.T) {
+	ob := NewOrderBook()
+	ob.AddBid(100, 1)
+	snapshot := ob.Snapshot()
+
+	snapshot.Bids[0].Price = 200 // Attempt to mutate snapshot
+
+	if ob.bids[1].Price == 200 {
+		t.Fatalf("expected internal bids to be immutable")
+	}
+}