diff --git a/tests/lock_manager_tests.cpp b/tests/lock_manager_tests.cpp
index e59ed496..eba498a2 100644
--- a/tests/lock_manager_tests.cpp
+++ b/tests/lock_manager_tests.cpp
@@ -126,4 +126,173 @@ TEST(LockManagerTests, Deadlock) {
     static_cast<void>(lm.unlock(&txn2, ridA));
 }
 
+// ============= New Tests =============
+
+/**
+ * @brief Verifies unlocking a non-existent lock returns false
+ */
+TEST(LockManagerTests, UnlockNonExistent) {
+    LockManager lm;
+    Transaction txn(1);
+    HeapTable::TupleId rid(1, 1);
+
+    // Unlock on non-existent lock should return false
+    EXPECT_FALSE(lm.unlock(&txn, rid));
+}
+
+/**
+ * @brief Verifies exclusive lock blocks shared lock acquisition
+ */
+TEST(LockManagerTests, ExclusiveBlocksShared) {
+    LockManager lm;
+    Transaction txn1(1);
+    Transaction txn2(2);
+    HeapTable::TupleId rid(1, 1);
+
+    // Acquire exclusive
+    EXPECT_TRUE(lm.acquire_exclusive(&txn1, rid));
+
+    // Shared should block (using try with immediate timeout behavior)
+    std::atomic<bool> shared_acquired{false};
+    std::thread t([&]() {
+        if (lm.acquire_shared(&txn2, rid)) {
+            shared_acquired = true;
+        }
+    });
+
+    // Give thread time to try acquiring
+    std::this_thread::sleep_for(TEST_SLEEP_MS);
+    EXPECT_FALSE(shared_acquired.load());
+
+    // Release exclusive
+    static_cast<void>(lm.unlock(&txn1, rid));
+
+    t.join();
+    EXPECT_TRUE(shared_acquired.load());
+    static_cast<void>(lm.unlock(&txn2, rid));
+}
+
+/**
+ * @brief Verifies shared lock blocks exclusive lock acquisition
+ */
+TEST(LockManagerTests, SharedBlocksExclusive) {
+    LockManager lm;
+    Transaction txn1(1);
+    Transaction txn2(2);
+    HeapTable::TupleId rid(1, 1);
+
+    // Acquire shared
+    EXPECT_TRUE(lm.acquire_shared(&txn1, rid));
+
+    // Exclusive should block
+    std::atomic<bool> exclusive_acquired{false};
+    std::thread t([&]() {
+        if (lm.acquire_exclusive(&txn2, rid)) {
+            exclusive_acquired = true;
+        }
+    });
+
+    // Give thread time to try acquiring
+    std::this_thread::sleep_for(TEST_SLEEP_MS);
+    EXPECT_FALSE(exclusive_acquired.load());
+
+    // Release shared
+    static_cast<void>(lm.unlock(&txn1, rid));
+
+    t.join();
+    EXPECT_TRUE(exclusive_acquired.load());
+    static_cast<void>(lm.unlock(&txn2, rid));
+}
+
+/**
+ * @brief Verifies unlock only releases the specific transaction's lock
+ */
+TEST(LockManagerTests, UnlockReleasesOnlyTxn) {
+    LockManager lm;
+    Transaction txn1(1);
+    Transaction txn2(2);
+    HeapTable::TupleId rid(1, 1);
+
+    // Two transactions acquire shared
+    EXPECT_TRUE(lm.acquire_shared(&txn1, rid));
+    EXPECT_TRUE(lm.acquire_shared(&txn2, rid));
+
+    // Unlock txn1 - should not affect txn2
+    static_cast<void>(lm.unlock(&txn1, rid));
+
+    // txn2 should still hold the lock - can still read
+    EXPECT_TRUE(lm.acquire_shared(&txn2, rid));
+
+    static_cast<void>(lm.unlock(&txn2, rid));
+}
+
+/**
+ * @brief Verifies lock re-acquisition by same transaction is idempotent
+ */
+TEST(LockManagerTests, LockSameRIDTwice) {
+    LockManager lm;
+    Transaction txn(1);
+    HeapTable::TupleId rid(1, 1);
+
+    // Lock manager allows re-acquisition by same transaction
+    EXPECT_TRUE(lm.acquire_shared(&txn, rid));
+    EXPECT_TRUE(lm.acquire_shared(&txn, rid));
+
+    // Should only need one unlock
+    static_cast<void>(lm.unlock(&txn, rid));
+}
+
+/**
+ * @brief Verifies three transactions can hold shared locks simultaneously
+ */
+TEST(LockManagerTests, MultipleSharedLocks) {
+    LockManager lm;
+    Transaction txn1(1);
+    Transaction txn2(2);
+    Transaction txn3(3);
+    HeapTable::TupleId rid(1, 1);
+
+    EXPECT_TRUE(lm.acquire_shared(&txn1, rid));
+    EXPECT_TRUE(lm.acquire_shared(&txn2, rid));
+    EXPECT_TRUE(lm.acquire_shared(&txn3, rid));
+
+    static_cast<void>(lm.unlock(&txn1, rid));
+    static_cast<void>(lm.unlock(&txn2, rid));
+    static_cast<void>(lm.unlock(&txn3, rid));
+}
+
+/**
+ * @brief Verifies transactions can hold locks on different RIDs independently
+ */
+TEST(LockManagerTests, LockDifferentRIDs) {
+    LockManager lm;
+    Transaction txn1(1);
+    Transaction txn2(2);
+    HeapTable::TupleId ridA(1, 1);
+    HeapTable::TupleId ridB(1, 2);
+
+    // txn1 gets exclusive on ridA, txn2 gets exclusive on ridB - both should succeed
+    EXPECT_TRUE(lm.acquire_exclusive(&txn1, ridA));
+    EXPECT_TRUE(lm.acquire_exclusive(&txn2, ridB));
+
+    static_cast<void>(lm.unlock(&txn1, ridA));
+    static_cast<void>(lm.unlock(&txn2, ridB));
+}
+
+/**
+ * @brief Verifies exclusive lock followed by shared on different RID succeeds
+ */
+TEST(LockManagerTests, ExclusiveThenShared) {
+    LockManager lm;
+    Transaction txn(1);
+    HeapTable::TupleId ridA(1, 1);
+    HeapTable::TupleId ridB(1, 2);
+
+    EXPECT_TRUE(lm.acquire_exclusive(&txn, ridA));
+    EXPECT_TRUE(lm.acquire_shared(&txn, ridB));
+
+    static_cast<void>(lm.unlock(&txn, ridA));
+    static_cast<void>(lm.unlock(&txn, ridB));
+}
+
 }  // namespace