1 files changed, 53 insertions, 0 deletions
diff --git a/internal/cache/clock/fuzz_test.go b/internal/cache/clock/fuzz_test.go
new file mode 100644
index 00000000..af0d4024
--- /dev/null
+++ b/internal/cache/clock/fuzz_test.go
@@ -0,0 +1,53 @@
+package clock //nolint:testpackage
+
+import "testing"
+
+// FuzzShard replays a decoded op stream against one shard,
+// checking the value oracle and invariants after every op.
+func FuzzShard(f *testing.F) {
+	f.Add([]byte{})
+	f.Add([]byte{0, 1, 10, 0, 2, 10, 0, 3, 10, 0, 4, 10, 1, 1, 0, 0, 5, 10})
+	f.Add([]byte{0, 7, 200, 0, 7, 5, 2, 7, 0, 3, 0, 0, 0, 8, 8})
+
+	f.Fuzz(func(t *testing.T, program []byte) {
+		const maxWeight = 32
+
+		shard := newShard[uint8, uint64](maxWeight)
+		shadow := make(map[uint8]uint64)
+
+		var nonce uint64
+
+		for i := 0; i+2 < len(program); i += 3 {
+			key := program[i+1]
+			weight := uint64(program[i+2])
+
+			switch program[i] % 4 {
+			case 0: // add
+				nonce++
+				value := nonce
+
+				admitted := shard.add(key, value, weight)
+				if admitted != (weight <= maxWeight) {
+					t.Fatalf("add(%d, w=%d) admitted=%v, want %v", key, weight, admitted, weight <= maxWeight)
+				}
+
+				if admitted {
+					shadow[key] = value
+				}
+			case 1: // get
+				if got, ok := shard.get(key); ok && got != shadow[key] {
+					t.Fatalf("get(%d) = %d, want %d", key, got, shadow[key])
+				}
+			case 2: // peek
+				if got, ok := shard.peek(key); ok && got != shadow[key] {
+					t.Fatalf("peek(%d) = %d, want %d", key, got, shadow[key])
+				}
+			case 3: // clear
+				shard.clear()
+				clear(shadow)
+			}
+
+			checkShard(t, shard)
+		}
+	})
+}