Added UI test cases for these scenarios to avoid future bugs like these.

app/src/androidTest/java/org/kiwix/kiwixmobile/reader/KiwixReaderFragmentTest.kt

@@ -46,11 +46,13 @@ import org.junit.Before
 import org.junit.Rule
 import org.junit.Test
 import org.kiwix.kiwixmobile.BaseActivityTest
+import org.kiwix.kiwixmobile.core.main.CoreMainActivity
 import org.kiwix.kiwixmobile.core.utils.LanguageUtils.Companion.handleLocaleChange
 import org.kiwix.kiwixmobile.core.utils.SharedPreferenceUtil
 import org.kiwix.kiwixmobile.core.utils.TestingUtils.COMPOSE_TEST_RULE_ORDER
 import org.kiwix.kiwixmobile.core.utils.TestingUtils.RETRY_RULE_ORDER
 import org.kiwix.kiwixmobile.main.KiwixMainActivity
+import org.kiwix.kiwixmobile.page.bookmarks.bookmarks
 import org.kiwix.kiwixmobile.testutils.RetryRule
 import org.kiwix.kiwixmobile.testutils.TestUtils
 import org.kiwix.kiwixmobile.testutils.TestUtils.closeSystemDialogs
@@ -115,6 +117,56 @@ class KiwixReaderFragmentTest : BaseActivityTest() {
     }
   }
 
+  @Test
+  fun testTabsRestoredAfterNavigatingLeftDrawerScreens() {
+    activityScenario.onActivity {
+      kiwixMainActivity = it
+      kiwixMainActivity.navigate(KiwixDestination.Library.route)
+    }
+    composeTestRule.waitForIdle()
+    val zimFile = getLocalZIMFile()
+    openKiwixReaderFragmentWithFile(zimFile)
+    reader {
+      checkZimFileLoadedSuccessful(composeTestRule)
+      // open a new tab
+      openSearchWithQuery("Android", zimFile)
+      openAndroidArticleInNewTab(composeTestRule)
+      checkZimFileLoadedSuccessful(composeTestRule)
+      // open bookmark screen.
+      bookmarks {
+        openBookmarkScreen(kiwixMainActivity as CoreMainActivity, composeTestRule)
+        assertBookMarksDisplayed(composeTestRule)
+      }
+      composeTestRule.waitForIdle()
+      pressBack()
+      assertTabsRestored(composeTestRule)
+    }
+  }
+
+  @Test
+  fun testTabsRestoredWhenNavigatingToOtherScreenViaBottomAppBar() {
+    activityScenario.onActivity {
+      kiwixMainActivity = it
+      kiwixMainActivity.navigate(KiwixDestination.Library.route)
+    }
+    composeTestRule.waitForIdle()
+    val zimFile = getLocalZIMFile()
+    openKiwixReaderFragmentWithFile(zimFile)
+    reader {
+      checkZimFileLoadedSuccessful(composeTestRule)
+      // open a new tab
+      openSearchWithQuery("Android", zimFile)
+      openAndroidArticleInNewTab(composeTestRule)
+      checkZimFileLoadedSuccessful(composeTestRule)
+      // open local library screen.
+      openLocalLibraryScreenViaBottomAppBar(composeTestRule)
+      composeTestRule.waitForIdle()
+      // press back to come back to reader screen.
+      pressBack()
+      assertTabsRestored(composeTestRule)
+    }
+  }
+
   @Test
   fun testTabClosedDialog() {
     activityScenario.onActivity {
@@ -122,26 +174,7 @@ class KiwixReaderFragmentTest : BaseActivityTest() {
       kiwixMainActivity.navigate(KiwixDestination.Library.route)
     }
     composeTestRule.waitForIdle()
-    val loadFileStream =
-      KiwixReaderFragmentTest::class.java.classLoader.getResourceAsStream("testzim.zim")
-    val zimFile =
-      File(
-        context.getExternalFilesDirs(null)[0],
-        "testzim.zim"
-      )
-    if (zimFile.exists()) zimFile.delete()
-    zimFile.createNewFile()
-    loadFileStream.use { inputStream ->
-      val outputStream: OutputStream = FileOutputStream(zimFile)
-      outputStream.use { it ->
-        val buffer = ByteArray(inputStream.available())
-        var length: Int
-        while (inputStream.read(buffer).also { length = it } > 0) {
-          it.write(buffer, 0, length)
-        }
-      }
-    }
-    openKiwixReaderFragmentWithFile(zimFile)
+    openKiwixReaderFragmentWithFile(getLocalZIMFile())
     composeTestRule.waitForIdle()
     reader {
       checkZimFileLoadedSuccessful(composeTestRule)
@@ -263,6 +296,43 @@ class KiwixReaderFragmentTest : BaseActivityTest() {
     }
   }
 
+  private fun getLocalZIMFile(): File {
+    val loadFileStream =
+      KiwixReaderFragmentTest::class.java.classLoader.getResourceAsStream("testzim.zim")
+    val zimFile =
+      File(
+        context.getExternalFilesDirs(null)[0],
+        "testzim.zim"
+      )
+    if (zimFile.exists()) zimFile.delete()
+    zimFile.createNewFile()
+    loadFileStream.use { inputStream ->
+      val outputStream: OutputStream = FileOutputStream(zimFile)
+      outputStream.use { it ->
+        val buffer = ByteArray(inputStream.available())
+        var length: Int
+        while (inputStream.read(buffer).also { length = it } > 0) {
+          it.write(buffer, 0, length)
+        }
+      }
+    }
+    return zimFile
+  }
+
+  private fun openSearchWithQuery(query: String = "", zimFile: File) {
+    UiThreadStatement.runOnUiThread {
+      if (zimFile.canRead()) {
+        kiwixMainActivity.openSearch(searchString = query)
+      } else {
+        throw RuntimeException(
+          "File $zimFile is not readable." +
+            " Original File $zimFile is readable = ${zimFile.canRead()}" +
+            " Size ${zimFile.length()}"
+        )
+      }
+    }
+  }
+
   private fun openKiwixReaderFragmentWithFile(zimFile: File) {
     UiThreadStatement.runOnUiThread {
       val navOptions = NavOptions.Builder()

app/src/androidTest/java/org/kiwix/kiwixmobile/reader/ReaderRobot.kt

@@ -35,6 +35,9 @@ import org.kiwix.kiwixmobile.core.main.reader.CLOSE_ALL_TABS_BUTTON_TESTING_TAG
 import org.kiwix.kiwixmobile.core.main.reader.READER_SCREEN_TESTING_TAG
 import org.kiwix.kiwixmobile.core.main.reader.TAB_MENU_ITEM_TESTING_TAG
 import org.kiwix.kiwixmobile.core.main.reader.TAB_TITLE_TESTING_TAG
+import org.kiwix.kiwixmobile.core.search.OPEN_ITEM_IN_NEW_TAB_ICON_TESTING_TAG
+import org.kiwix.kiwixmobile.main.BOTTOM_NAV_LIBRARY_ITEM_TESTING_TAG
+import org.kiwix.kiwixmobile.core.main.reader.TABS_SIZE_TEXT_TESTING_TAG
 import org.kiwix.kiwixmobile.testutils.TestUtils
 import org.kiwix.kiwixmobile.testutils.TestUtils.testFlakyView
 import org.kiwix.kiwixmobile.testutils.TestUtils.waitUntilTimeout
@@ -115,4 +118,31 @@ class ReaderRobot : BaseRobot() {
         )
     })
   }
+
+  fun openAndroidArticleInNewTab(composeTestRule: ComposeContentTestRule) {
+    testFlakyView({
+      composeTestRule.apply {
+        waitForIdle()
+        onAllNodesWithTag(OPEN_ITEM_IN_NEW_TAB_ICON_TESTING_TAG)[0].performClick()
+      }
+    })
+  }
+
+  fun assertTabsRestored(composeTestRule: ComposeContentTestRule) {
+    testFlakyView({
+      composeTestRule.apply {
+        waitForIdle()
+        onNodeWithTag(TABS_SIZE_TEXT_TESTING_TAG, useUnmergedTree = true).assertTextEquals("2")
+      }
+    })
+  }
+
+  fun openLocalLibraryScreenViaBottomAppBar(composeTestRule: ComposeContentTestRule) {
+    testFlakyView({
+      composeTestRule.apply {
+        waitForIdle()
+        onNodeWithTag(BOTTOM_NAV_LIBRARY_ITEM_TESTING_TAG).performClick()
+      }
+    })
+  }
 }

core/src/main/java/org/kiwix/kiwixmobile/core/main/reader/ReaderMenuState.kt

@@ -35,6 +35,7 @@ import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
+import androidx.compose.ui.platform.testTag
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextOverflow
 import org.kiwix.kiwixmobile.core.R
@@ -57,6 +58,7 @@ const val TAKE_NOTE_MENU_ITEM_TESTING_TAG = "takeNoteMenuItemTestingTag"
 const val FULL_SCREEN_MENU_ITEM_TESTING_TAG = "fullScreenMenuItemTestingTag"
 const val RANDOM_ARTICLE_MENU_ITEM_TESTING_TAG = "randomArticleMenuItemTestingTag"
 const val TAB_MENU_ITEM_TESTING_TAG = "tabMenuItemTestingTag"
+const val TABS_SIZE_TEXT_TESTING_TAG = "tabsSizeTextTestingTag"
 
 @Stable
 class ReaderMenuState(
@@ -227,7 +229,8 @@ class ReaderMenuState(
           fontWeight = FontWeight.Bold,
           fontSize = TAB_SWITCHER_TEXT_SIZE,
           maxLines = 1,
-          overflow = TextOverflow.Ellipsis
+          overflow = TextOverflow.Ellipsis,
+          modifier = Modifier.testTag(TABS_SIZE_TEXT_TESTING_TAG)
         )
       }
     }

core/src/main/java/org/kiwix/kiwixmobile/core/search/SearchScreen.kt

@@ -50,6 +50,7 @@ import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.platform.LocalLayoutDirection
+import androidx.compose.ui.platform.testTag
 import androidx.compose.ui.res.painterResource
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.semantics.semantics
@@ -73,6 +74,7 @@ const val SEARCH_FIELD_TESTING_TAG = "searchFieldTestingTag"
 const val NO_SEARCH_RESULT_TESTING_TAG = "noSearchResultTestingTag"
 const val FIND_IN_PAGE_TESTING_TAG = "findInPageTestingTag"
 const val SEARCH_ITEM_TESTING_TAG = "searchItemTestingTag"
+const val OPEN_ITEM_IN_NEW_TAB_ICON_TESTING_TAG = "openItemInNewTagIconTestingTag"
 const val LOADING_ITEMS_BEFORE = 3
 
 @OptIn(ExperimentalMaterial3Api::class)
@@ -232,6 +234,7 @@ private fun SearchListItem(
 
     IconButton(
       onClick = { onNewTabIconClick(searchListItem) },
+      modifier = Modifier.testTag(OPEN_ITEM_IN_NEW_TAB_ICON_TESTING_TAG)
     ) {
       Icon(
         painter = painterResource(id = R.drawable.ic_open_in_new_24dp),