diff --git a/src/lib/ledger.ts b/src/lib/ledger.ts
index f6a1130..00e34fd 100644
--- a/src/lib/ledger.ts
+++ b/src/lib/ledger.ts
@@ -17,7 +17,6 @@ import {
   LOCK_DEFAULT_INITIAL_RETRY_INTERVAL_MS,
   LOCK_DEFAULT_MAX_RETRIES,
   LOCK_STALE_TIMEOUT_MS,
-  LOCKED_BYTES,
   LOCKED_BYTES_LENGTH,
   SUPPORTED_LEDGER_VERSIONS,
   UNLOCKED_BYTES,
@@ -489,7 +488,7 @@ export class KVLedger {
           currentOffset += result.length + result.errorCorrectionOffset;
 
           // Update the header after each read, to make sure we catch any new transactions
-          this.readHeader();
+          await this.readHeader();
         } else if (!ignoreReadErrors) {
           throw new Error("Unexpected end of file");
         }
@@ -637,7 +636,7 @@ export class KVLedger {
         }
 
         // 2. Prepare lock data
-        const lockBytes = LOCKED_BYTES;
+        const lockBytes = new Uint8Array(LOCKED_BYTES_LENGTH);
         const lockView = new DataView(lockBytes.buffer);
         const lockId = pseudoRandomTimestamp(BigInt(Date.now()), 11); // A lock id is a regular timestamp with the last 11 bits scrambled
         lockView.setBigUint64(0, lockId, false);
diff --git a/src/lib/transaction.ts b/src/lib/transaction.ts
index 6c6904f..e4486f3 100644
--- a/src/lib/transaction.ts
+++ b/src/lib/transaction.ts
@@ -138,7 +138,7 @@ export class KVTransaction {
     algorithm?: KVHashAlgorithm,
   ) {
     // Validate
-    if (this.operation === KVOperation.SET && value === undefined) {
+    if (operation === KVOperation.SET && value === undefined) {
       throw new Error("Set operation needs data");
     }
     this.key = key;
diff --git a/test/index.test.ts b/test/index.test.ts
new file mode 100644
index 0000000..2449d9c
--- /dev/null
+++ b/test/index.test.ts
@@ -0,0 +1,232 @@
+import { assertEquals } from "@std/assert";
+import { test } from "@cross/test";
+import { KVIndex } from "../src/lib/index.ts";
+import { KVKeyInstance } from "../src/lib/key.ts";
+
+test("KVIndex: add and get single entry", () => {
+  const index = new KVIndex();
+  const key = new KVKeyInstance(["users", "alice"]);
+  index.add(key, 100);
+
+  const results = index.get(new KVKeyInstance(["users", "alice"], true));
+  assertEquals(results, [100]);
+});
+
+test("KVIndex: get returns empty array for missing key", () => {
+  const index = new KVIndex();
+  const results = index.get(new KVKeyInstance(["nonexistent"], true));
+  assertEquals(results, []);
+});
+
+test("KVIndex: add overwrites existing entry at same key", () => {
+  const index = new KVIndex();
+  const key1 = new KVKeyInstance(["users", "alice"]);
+  const key2 = new KVKeyInstance(["users", "alice"]);
+  index.add(key1, 100);
+  index.add(key2, 200);
+
+  const results = index.get(new KVKeyInstance(["users", "alice"], true));
+  assertEquals(results, [200]);
+});
+
+test("KVIndex: get multiple entries under common prefix", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["users", "alice"]), 100);
+  index.add(new KVKeyInstance(["users", "bob"]), 200);
+  index.add(new KVKeyInstance(["users", "carol"]), 300);
+
+  const results = index.get(new KVKeyInstance(["users"], true));
+  assertEquals(results.sort((a, b) => a - b), [100, 200, 300]);
+});
+
+test("KVIndex: get returns results sorted by offset (ascending)", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["data", "c"]), 300);
+  index.add(new KVKeyInstance(["data", "a"]), 100);
+  index.add(new KVKeyInstance(["data", "b"]), 200);
+
+  const results = index.get(new KVKeyInstance(["data"], true));
+  assertEquals(results, [100, 200, 300]);
+});
+
+test("KVIndex: get returns results sorted by offset (descending) when reverse=true", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["data", "c"]), 300);
+  index.add(new KVKeyInstance(["data", "a"]), 100);
+  index.add(new KVKeyInstance(["data", "b"]), 200);
+
+  const results = index.get(new KVKeyInstance(["data"], true), undefined, true);
+  assertEquals(results, [300, 200, 100]);
+});
+
+test("KVIndex: get respects limit", () => {
+  const index = new KVIndex();
+  for (let i = 1; i <= 5; i++) {
+    index.add(new KVKeyInstance(["data", i]), i * 10);
+  }
+
+  const results = index.get(new KVKeyInstance(["data"], true), 3);
+  assertEquals(results.length, 3);
+  assertEquals(results, [10, 20, 30]);
+});
+
+test("KVIndex: get with numeric range", () => {
+  const index = new KVIndex();
+  for (let i = 1; i <= 10; i++) {
+    index.add(new KVKeyInstance(["scores", i]), i * 100);
+  }
+
+  const results = index.get(
+    new KVKeyInstance(["scores", { from: 3, to: 6 }], true),
+  );
+  assertEquals(results.sort((a, b) => a - b), [300, 400, 500, 600]);
+});
+
+test("KVIndex: get with string range", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["files", "doc-a"]), 100);
+  index.add(new KVKeyInstance(["files", "doc-b"]), 200);
+  index.add(new KVKeyInstance(["files", "img-1"]), 300);
+
+  const results = index.get(
+    new KVKeyInstance(["files", { from: "doc-a", to: "doc-z" }], true),
+  );
+  assertEquals(results.sort((a, b) => a - b), [100, 200]);
+});
+
+test("KVIndex: get with empty range matches all children", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["items", 1]), 10);
+  index.add(new KVKeyInstance(["items", 2]), 20);
+  index.add(new KVKeyInstance(["items", 3]), 30);
+
+  const results = index.get(new KVKeyInstance(["items", {}], true));
+  assertEquals(results.sort((a, b) => a - b), [10, 20, 30]);
+});
+
+test("KVIndex: delete removes entry", () => {
+  const index = new KVIndex();
+  const key = new KVKeyInstance(["users", "alice"]);
+  index.add(key, 100);
+
+  const removed = index.delete(new KVKeyInstance(["users", "alice"]));
+  assertEquals(removed, 100);
+
+  const results = index.get(new KVKeyInstance(["users", "alice"], true));
+  assertEquals(results, []);
+});
+
+test("KVIndex: delete returns undefined for missing key", () => {
+  const index = new KVIndex();
+  const removed = index.delete(new KVKeyInstance(["nonexistent"]));
+  assertEquals(removed, undefined);
+});
+
+test("KVIndex: delete cleans up empty parent nodes", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["users", "alice", "profile"]), 100);
+  index.delete(new KVKeyInstance(["users", "alice", "profile"]));
+
+  // Parent nodes should be gone
+  const results = index.get(new KVKeyInstance(["users"], true));
+  assertEquals(results, []);
+  assertEquals(index.getChildKeys(null), []);
+});
+
+test("KVIndex: delete keeps sibling nodes intact", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["users", "alice"]), 100);
+  index.add(new KVKeyInstance(["users", "bob"]), 200);
+
+  index.delete(new KVKeyInstance(["users", "alice"]));
+
+  const remaining = index.get(new KVKeyInstance(["users"], true));
+  assertEquals(remaining, [200]);
+});
+
+test("KVIndex: clear removes all entries", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["a"]), 1);
+  index.add(new KVKeyInstance(["b"]), 2);
+
+  index.clear();
+
+  assertEquals(index.get(new KVKeyInstance(["a"], true)), []);
+  assertEquals(index.get(new KVKeyInstance(["b"], true)), []);
+  assertEquals(index.getChildKeys(null), []);
+});
+
+test("KVIndex: setIndex replaces entire index", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["old"]), 999);
+
+  const newIndex = new KVIndex();
+  newIndex.add(new KVKeyInstance(["new"]), 42);
+  index.setIndex(newIndex.index);
+
+  assertEquals(index.get(new KVKeyInstance(["old"], true)), []);
+  assertEquals(index.get(new KVKeyInstance(["new"], true)), [42]);
+});
+
+test("KVIndex: getChildKeys returns root-level keys when null is passed", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["users", "alice"]), 100);
+  index.add(new KVKeyInstance(["products", 1]), 200);
+  index.add(new KVKeyInstance(["settings"]), 300);
+
+  const keys = index.getChildKeys(null).sort();
+  assertEquals(keys, ["products", "settings", "users"]);
+});
+
+test("KVIndex: getChildKeys returns child keys for a given key", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["user", "name"]), 100);
+  index.add(new KVKeyInstance(["user", "age"]), 200);
+  index.add(new KVKeyInstance(["user", "email"]), 300);
+
+  const keys = index.getChildKeys(new KVKeyInstance(["user"])).sort();
+  assertEquals(keys, ["age", "email", "name"]);
+});
+
+test("KVIndex: getChildKeys returns empty array for nonexistent key", () => {
+  const index = new KVIndex();
+  const keys = index.getChildKeys(new KVKeyInstance(["nonexistent"]));
+  assertEquals(keys, []);
+});
+
+test("KVIndex: getChildKeys converts numeric keys to strings", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["items", 1]), 10);
+  index.add(new KVKeyInstance(["items", 2]), 20);
+
+  const keys = index.getChildKeys(new KVKeyInstance(["items"])).sort();
+  assertEquals(keys, ["1", "2"]);
+});
+
+test("KVIndex: handles multi-level keys with numbers", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["data", "user", 4]), 100);
+  index.add(new KVKeyInstance(["data", "system", 4]), 200);
+
+  assertEquals(
+    index.get(new KVKeyInstance(["data", "user", 4], true)),
+    [100],
+  );
+  assertEquals(
+    index.get(new KVKeyInstance(["data", "system", 4], true)),
+    [200],
+  );
+  assertEquals(
+    index.get(new KVKeyInstance(["data", "system", 5], true)),
+    [],
+  );
+});
+
+test("KVIndex: get with limit 0 returns empty array", () => {
+  const index = new KVIndex();
+  index.add(new KVKeyInstance(["data", 1]), 10);
+  index.add(new KVKeyInstance(["data", 2]), 20);
+
+  const results = index.get(new KVKeyInstance(["data"], true), 0);
+  assertEquals(results, []);
+});
diff --git a/test/randomts.test.ts b/test/randomts.test.ts
new file mode 100644
index 0000000..81c078c
--- /dev/null
+++ b/test/randomts.test.ts
@@ -0,0 +1,58 @@
+import { assertEquals } from "@std/assert";
+import { test } from "@cross/test";
+import { pseudoRandomTimestamp } from "../src/lib/utils/randomts.ts";
+
+test("pseudoRandomTimestamp: returns a bigint", () => {
+  const ts = pseudoRandomTimestamp(BigInt(Date.now()));
+  assertEquals(typeof ts, "bigint");
+});
+
+test("pseudoRandomTimestamp: result is close to original timestamp", () => {
+  const original = BigInt(Date.now());
+  const result = pseudoRandomTimestamp(original);
+
+  // The upper bits should be preserved (only bottom numBits are randomized)
+  // With numBits=11, the mask clears the lower 11 bits (~2047), so the
+  // result should be within 2048 of the original
+  const diff = result > original ? result - original : original - result;
+  assertEquals(diff < BigInt(2048), true);
+});
+
+test("pseudoRandomTimestamp: produces different values on repeated calls", () => {
+  const ts = BigInt(Date.now());
+  const results = new Set<bigint>();
+
+  // Generate multiple values; they should not all be the same
+  for (let i = 0; i < 20; i++) {
+    results.add(pseudoRandomTimestamp(ts));
+  }
+
+  // With 11 bits of randomness (2048 possible values), 20 calls should
+  // almost certainly produce more than one unique value
+  assertEquals(results.size > 1, true);
+});
+
+test("pseudoRandomTimestamp: custom numBits works", () => {
+  const original = BigInt(1000000);
+  const result = pseudoRandomTimestamp(original, 4);
+
+  // With numBits=4, only the bottom 4 bits (0–15) are randomized
+  const diff = result > original ? result - original : original - result;
+  assertEquals(diff < BigInt(16), true);
+});
+
+test("pseudoRandomTimestamp: zero timestamp produces a bigint", () => {
+  const result = pseudoRandomTimestamp(BigInt(0));
+  assertEquals(typeof result, "bigint");
+  // With 0 input and 11-bit randomness, result should be < 2048
+  assertEquals(result < BigInt(2048), true);
+});
+
+test("pseudoRandomTimestamp: preserves upper bits of large timestamp", () => {
+  const original = BigInt("0x7FFFFFFFFFFFFFFF"); // Large 63-bit value
+  const result = pseudoRandomTimestamp(original, 11);
+  const mask = BigInt(~((1 << 11) - 1));
+
+  // Upper bits should match
+  assertEquals((result & mask) === (original & mask), true);
+});
diff --git a/test/transaction.test.ts b/test/transaction.test.ts
index 032b348..038d5c8 100644
--- a/test/transaction.test.ts
+++ b/test/transaction.test.ts
@@ -422,3 +422,25 @@ test("KVTransaction: incorrect hash algorithm throws error", () => {
     "Incorrect hash algorithm requested",
   );
 });
+
+test("KVTransaction: SET with undefined value throws error", () => {
+  // Arrange
+  const key = new KVKeyInstance(["test"]);
+  const timestamp = Date.now();
+
+  // Act & Assert: SET without a value should throw
+  const transaction = new KVTransaction();
+  assertThrows(
+    () => {
+      transaction.create(
+        key,
+        KVOperation.SET,
+        timestamp,
+        undefined,
+        KVHashAlgorithm.MURMURHASH3,
+      );
+    },
+    Error,
+    "Set operation needs data",
+  );
+});