diff --git a/tests/test_optimized_kernel.py b/tests/test_optimized_kernel.py
new file mode 100644
index 0000000..5f6d217
--- /dev/null
+++ b/tests/test_optimized_kernel.py
@@ -0,0 +1,93 @@
+"""Tests for optimized kernel system - covers gaps not in test_main_utils.py::TestOptimizedKernel."""
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+
+@pytest.fixture
+def main_module(hc_module):
+    return hc_module._main
+
+
+class TestOptimizedKernelMissingNames:
+    """Covers the two DEFAULT_OPTIMIZED_ATTACKS names missing from test_main_utils.py."""
+
+    @pytest.mark.parametrize(
+        "attack_name",
+        [
+            "hcatAdHocMask",
+            "hcatMarkovBruteForce",
+        ],
+    )
+    def test_optimized_attacks_return_true(self, main_module, attack_name):
+        assert main_module._should_use_optimized_kernel(attack_name) is True
+
+
+class TestOptimizedKernelNonMembers:
+    """Covers False cases not already parametrized in test_main_utils.py."""
+
+    @pytest.mark.parametrize(
+        "attack_name",
+        [
+            "hcatOllama",
+            "hcatNgramX",
+            "hcatGenerateRules",
+            "hcatMarkovTrain",
+            "hcatOmenTrain",
+            "unknown_attack",
+        ],
+    )
+    def test_non_optimized_attacks_return_false(self, main_module, attack_name):
+        assert main_module._should_use_optimized_kernel(attack_name) is False
+
+
+class TestHcatFingerprintOptimizedFlag:
+    """End-to-end mock test verifying hcatFingerprint passes -O to hashcat."""
+
+    def test_fingerprint_includes_optimized_flag(self, main_module, tmp_path):
+        hash_file = tmp_path / "hashes.txt"
+        hash_file.write_text("")
+        (tmp_path / "hashes.txt.out").write_text("")
+        # hcatFingerprint opens .working and .expanded inside the loop; create them.
+        (tmp_path / "hashes.txt.working").write_text("")
+        (tmp_path / "hashes.txt.expanded").write_text("")
+
+        captured_cmds = []
+
+        def fake_popen(cmd, **kwargs):
+            captured_cmds.append(list(cmd))
+            proc = MagicMock()
+            proc.stdout = MagicMock()
+            proc.pid = 1234
+            proc.wait.return_value = 0
+            return proc
+
+        # lineCount call sequence:
+        #   call 1 (initial, before loop): 1  -> crackedBefore=1, crackedAfter=0 -> enter loop
+        #   call 2 (top of loop body):     1  -> crackedBefore=1
+        #   call 3 (bottom of loop body):  1  -> crackedAfter=1 -> exit loop (1==1)
+        #   call 4 (final hcatFingerprintCount assignment): 1
+        with (
+            patch("hate_crack.main.subprocess.Popen", side_effect=fake_popen),
+            patch.object(main_module, "hcatBin", "hashcat"),
+            patch.object(main_module, "hcatTuning", ""),
+            patch.object(main_module, "hcatPotfilePath", ""),
+            patch.object(main_module, "hate_path", str(tmp_path)),
+            patch.object(main_module, "hcatExpanderBin", "expander.bin"),
+            patch.object(main_module, "hcatHashCracked", 0),
+            patch("hate_crack.main.lineCount", side_effect=[1, 1, 1, 1]),
+            patch("hate_crack.main._write_delimited_field"),
+            patch("hate_crack.main.ensure_binary"),
+            patch("hate_crack.main.generate_session_id", return_value="test_session"),
+        ):
+            main_module.hcatFingerprint(
+                hcatHashType="1000",
+                hcatHashFile=str(hash_file),
+            )
+
+        hashcat_cmds = [cmd for cmd in captured_cmds if cmd and cmd[0] == "hashcat"]
+        assert hashcat_cmds, "No hashcat Popen calls captured"
+        assert any("-O" in cmd for cmd in hashcat_cmds), (
+            f"Expected -O in hashcat cmd, got: {hashcat_cmds}"
+        )