test: add verification for MultiBackstack navigation logic

core/navigation/src/commonTest/kotlin/org/meshtastic/core/navigation/MultiBackstackTest.kt

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.core.navigation
+
+import androidx.navigation3.runtime.NavBackStack
+import androidx.navigation3.runtime.NavKey
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class MultiBackstackTest {
+
+    @Test
+    fun `navigateTopLevel to different tab preserves previous tab stack and activates new tab stack`() {
+        val startTab = TopLevelDestination.Nodes.route
+        val multiBackstack = MultiBackstack(startTab)
+
+        val nodesStack =
+            NavBackStack<NavKey>().apply { addAll(listOf(TopLevelDestination.Nodes.route, NodesRoutes.Nodes)) }
+        val mapStack = NavBackStack<NavKey>().apply { addAll(listOf(TopLevelDestination.Map.route)) }
+
+        multiBackstack.backStacks =
+            mapOf(TopLevelDestination.Nodes.route to nodesStack, TopLevelDestination.Map.route to mapStack)
+
+        assertEquals(TopLevelDestination.Nodes.route, multiBackstack.currentTabRoute)
+        assertEquals(2, multiBackstack.activeBackStack.size)
+
+        multiBackstack.navigateTopLevel(TopLevelDestination.Map.route)
+
+        assertEquals(TopLevelDestination.Map.route, multiBackstack.currentTabRoute)
+        assertEquals(1, multiBackstack.activeBackStack.size)
+        assertEquals(2, nodesStack.size)
+    }
+
+    @Test
+    fun `navigateTopLevel to same tab resets stack to root`() {
+        val startTab = TopLevelDestination.Nodes.route
+        val multiBackstack = MultiBackstack(startTab)
+
+        val nodesStack =
+            NavBackStack<NavKey>().apply { addAll(listOf(TopLevelDestination.Nodes.route, NodesRoutes.Nodes)) }
+        multiBackstack.backStacks = mapOf(TopLevelDestination.Nodes.route to nodesStack)
+
+        assertEquals(2, multiBackstack.activeBackStack.size)
+
+        multiBackstack.navigateTopLevel(TopLevelDestination.Nodes.route)
+
+        assertEquals(1, multiBackstack.activeBackStack.size)
+        assertEquals(TopLevelDestination.Nodes.route, multiBackstack.activeBackStack.first())
+    }
+
+    @Test
+    fun `goBack pops current stack if size is greater than 1`() {
+        val startTab = TopLevelDestination.Nodes.route
+        val multiBackstack = MultiBackstack(startTab)
+
+        val nodesStack =
+            NavBackStack<NavKey>().apply { addAll(listOf(TopLevelDestination.Nodes.route, NodesRoutes.Nodes)) }
+        multiBackstack.backStacks = mapOf(TopLevelDestination.Nodes.route to nodesStack)
+
+        multiBackstack.goBack()
+
+        assertEquals(1, multiBackstack.activeBackStack.size)
+        assertEquals(TopLevelDestination.Nodes.route, multiBackstack.activeBackStack.first())
+    }
+
+    @Test
+    fun `goBack on root of non-start tab returns to start tab`() {
+        val startTab = TopLevelDestination.Connections.route
+        val multiBackstack = MultiBackstack(startTab)
+
+        val mapStack = NavBackStack<NavKey>().apply { addAll(listOf(TopLevelDestination.Map.route)) }
+        val connectionsStack = NavBackStack<NavKey>().apply { addAll(listOf(TopLevelDestination.Connections.route)) }
+
+        multiBackstack.backStacks =
+            mapOf(TopLevelDestination.Map.route to mapStack, TopLevelDestination.Connections.route to connectionsStack)
+
+        multiBackstack.navigateTopLevel(TopLevelDestination.Map.route)
+        assertEquals(TopLevelDestination.Map.route, multiBackstack.currentTabRoute)
+
+        multiBackstack.goBack()
+
+        assertEquals(TopLevelDestination.Connections.route, multiBackstack.currentTabRoute)
+    }
+
+    @Test
+    fun `handleDeepLink sets target tab and populates stack`() {
+        val startTab = TopLevelDestination.Nodes.route
+        val multiBackstack = MultiBackstack(startTab)
+
+        val settingsStack = NavBackStack<NavKey>().apply { addAll(listOf(TopLevelDestination.Settings.route)) }
+        multiBackstack.backStacks = mapOf(TopLevelDestination.Settings.route to settingsStack)
+
+        val deepLinkPath = listOf(TopLevelDestination.Settings.route, SettingsRoutes.About)
+        multiBackstack.handleDeepLink(deepLinkPath)
+
+        assertEquals(TopLevelDestination.Settings.route, multiBackstack.currentTabRoute)
+        assertEquals(2, multiBackstack.activeBackStack.size)
+        assertEquals(SettingsRoutes.About, multiBackstack.activeBackStack.last())
+    }
+}