diff --git a/tests/test_dxvk_fps_limit.py b/tests/test_dxvk_fps_limit.py
index 4dc5856..5b864a3 100644
--- a/tests/test_dxvk_fps_limit.py
+++ b/tests/test_dxvk_fps_limit.py
@@ -1,5 +1,7 @@
+import ctypes
 import os
 import tempfile
+import types
 import unittest
 from unittest import mock
 
@@ -30,6 +32,41 @@ class DxvkFpsLimitTests(unittest.TestCase):
         with open(path, "r", encoding="utf-8") as handle:
             return handle.read()
 
+    def detect_with_fake_displays(self, devices, default=77):
+        """Run Windows display detection against deterministic fake Win32 APIs."""
+        # Each record is (device name, state flags, refresh rate, settings_ok).
+        def enum_display_devices(_device, index, device_ptr, _flags):
+            if index >= len(devices):
+                return False
+            name, state_flags, _rate, _settings_ok = devices[index]
+            device_ptr._obj.DeviceName = name
+            device_ptr._obj.StateFlags = state_flags
+            return True
+
+        def enum_display_settings(device_name, _mode, mode_ptr):
+            for name, _state_flags, rate, settings_ok in devices:
+                if name != device_name:
+                    continue
+                if not settings_ok:
+                    return False
+                mode_ptr._obj.dmDisplayFrequency = rate
+                return True
+            return False
+
+        fake_user32 = types.SimpleNamespace(
+            EnumDisplayDevicesW=enum_display_devices,
+            EnumDisplaySettingsW=enum_display_settings,
+        )
+        fake_windll = types.SimpleNamespace(user32=fake_user32)
+
+        with mock.patch.object(dxvk_fps.os, "name", "nt"), mock.patch.object(
+            ctypes,
+            "windll",
+            fake_windll,
+            create=True,
+        ):
+            return dxvk_fps.detect_max_refresh_rate(default=default)
+
     def test_enable_replaces_bundled_commented_value_and_preserves_other_options(self):
         with tempfile.TemporaryDirectory() as root:
             path = self.write_config(
@@ -79,6 +116,24 @@ class DxvkFpsLimitTests(unittest.TestCase):
             self.assertIn("d3d9.maxFrameRate = 240\n", updated)
             self.assertIn("dxvk.allowFse = False\n", updated)
 
+    def test_signed_legacy_values_are_replaced_without_duplicates(self):
+        with tempfile.TemporaryDirectory() as root:
+            path = self.write_config(
+                root,
+                "d3d9.maxFrameRate = -120\n"
+                "# d3d9.maxFrameRate = +90\n"
+                "dxvk.allowFse = False\n",
+            )
+
+            dxvk_fps.apply_dxvk_fps_limit(path, True, 165)
+            updated = self.read_config(path)
+
+            self.assertEqual(updated.count("d3d9.maxFrameRate"), 1)
+            self.assertIn("d3d9.maxFrameRate = 165\n", updated)
+            self.assertNotIn("-120", updated)
+            self.assertNotIn("+90", updated)
+            self.assertIn("dxvk.allowFse = False\n", updated)
+
     def test_missing_limit_line_is_appended(self):
         with tempfile.TemporaryDirectory() as root:
             path = self.write_config(root, "dxvk.allowFse = False\n")
@@ -99,6 +154,34 @@ class DxvkFpsLimitTests(unittest.TestCase):
 
             self.assertEqual(self.read_config(path), original)
 
+    def test_refresh_detection_uses_fastest_attached_valid_display(self):
+        detected = self.detect_with_fake_displays(
+            [
+                ("DISPLAY1", 0x00000001, 60, True),
+                # Faster but not attached to the desktop: must be ignored.
+                ("DISPLAY2", 0x00000000, 360, True),
+                ("DISPLAY3", 0x00000001, 165, True),
+                # Windows unknown/default frequency: must be ignored.
+                ("DISPLAY4", 0x00000001, 1, True),
+                # Current settings query failed: must be ignored.
+                ("DISPLAY5", 0x00000001, 240, False),
+            ],
+            default=77,
+        )
+        self.assertEqual(detected, 165)
+
+    def test_refresh_detection_falls_back_when_no_usable_display_rate_exists(self):
+        detected = self.detect_with_fake_displays(
+            [
+                ("DISPLAY1", 0x00000000, 240, True),
+                ("DISPLAY2", 0x00000001, 0, True),
+                ("DISPLAY3", 0x00000001, 1, True),
+                ("DISPLAY4", 0x00000001, 165, False),
+            ],
+            default=77,
+        )
+        self.assertEqual(detected, 77)
+
     def test_refresh_detection_always_returns_a_positive_integer(self):
         detected = dxvk_fps.detect_max_refresh_rate(default=77)
         self.assertIsInstance(detected, int)