diff --git a/sharedUI/src/commonTest/kotlin/org/shahondin1624/ResponsiveNavigationModeTest.kt b/sharedUI/src/commonTest/kotlin/org/shahondin1624/ResponsiveNavigationModeTest.kt
new file mode 100644
index 0000000..2b8e0c9
--- /dev/null
+++ b/sharedUI/src/commonTest/kotlin/org/shahondin1624/ResponsiveNavigationModeTest.kt
@@ -0,0 +1,95 @@
+package org.shahondin1624
+
+import androidx.compose.foundation.layout.BoxWithConstraints
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.width
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.test.ExperimentalTestApi
+import androidx.compose.ui.test.assertIsDisplayed
+import androidx.compose.ui.test.onAllNodesWithTag
+import androidx.compose.ui.test.onNodeWithTag
+import androidx.compose.ui.test.performClick
+import androidx.compose.ui.test.runComposeUiTest
+import androidx.compose.ui.unit.dp
+import org.shahondin1624.lib.components.TestTags
+import org.shahondin1624.theme.LocalWindowSizeClass
+import org.shahondin1624.theme.WindowSizeClass
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/**
+ * Tests that the correct navigation mode is rendered at each window size class.
+ */
+@OptIn(ExperimentalTestApi::class)
+class ResponsiveNavigationModeTest {
+
+    @Test
+    fun compactShowsModalDrawerHiddenByDefault() = runComposeUiTest {
+        setContent {
+            App()
+        }
+
+        waitForIdle()
+
+        // Hamburger menu button should be visible
+        onNodeWithTag(TestTags.MENU_BUTTON).assertIsDisplayed()
+
+        // Navigation rail and permanent drawer should not exist
+        assertEquals(
+            0,
+            onAllNodesWithTag(TestTags.NAV_RAIL).fetchSemanticsNodes().size,
+            "NavigationRail should not be present in compact mode"
+        )
+        assertEquals(
+            0,
+            onAllNodesWithTag(TestTags.NAV_PERMANENT_DRAWER).fetchSemanticsNodes().size,
+            "PermanentDrawer should not be present in compact mode"
+        )
+    }
+
+    @Test
+    fun compactDrawerAppearsOnMenuTap() = runComposeUiTest {
+        setContent {
+            App()
+        }
+
+        waitForIdle()
+
+        // Tap hamburger
+        onNodeWithTag(TestTags.MENU_BUTTON).performClick()
+        waitForIdle()
+
+        // Drawer content should now be visible
+        onNodeWithTag(TestTags.NAV_CHARACTER_SHEET).assertIsDisplayed()
+        onNodeWithTag(TestTags.NAV_SETTINGS).assertIsDisplayed()
+    }
+
+    @Test
+    fun expandedShowsPermanentSidebar() = runComposeUiTest {
+        setContent {
+            // Force expanded size class by wrapping in a wide box
+            CompositionLocalProvider(LocalWindowSizeClass provides WindowSizeClass.Expanded) {
+                BoxWithConstraints(modifier = Modifier.width(1200.dp).fillMaxSize()) {
+                    App()
+                }
+            }
+        }
+
+        waitForIdle()
+
+        // Permanent drawer should be visible
+        onNodeWithTag(TestTags.NAV_PERMANENT_DRAWER).assertIsDisplayed()
+
+        // Hamburger menu button should not exist
+        assertEquals(
+            0,
+            onAllNodesWithTag(TestTags.MENU_BUTTON).fetchSemanticsNodes().size,
+            "Menu button should not be present in expanded mode"
+        )
+
+        // Navigation items always visible
+        onNodeWithTag(TestTags.NAV_CHARACTER_SHEET).assertIsDisplayed()
+        onNodeWithTag(TestTags.NAV_SETTINGS).assertIsDisplayed()
+    }
+}