Prevent mailbox reload when expanding active folder

ET-6199

mail-mailbox/presentation/src/main/kotlin/ch/protonmail/android/mailmailbox/presentation/mailbox/MailboxViewModel.kt

@@ -150,6 +150,7 @@ import kotlinx.coroutines.flow.channelFlow
 import kotlinx.coroutines.flow.collect
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.distinctUntilChangedBy
 import kotlinx.coroutines.flow.drop
 import kotlinx.coroutines.flow.filter
 import kotlinx.coroutines.flow.filterNotNull
@@ -1439,7 +1440,7 @@ class MailboxViewModel @Inject constructor(
 
     private fun observeMailLabelChangeRequests(): Flow<MailLabel> = observeSelectedMailLabelId()
         .mapToExistingLabel()
-        .distinctUntilChanged()
+        .distinctUntilChangedBy { it.id }
 
     private fun Flow<MailboxState>.observeSearchQuery() = this.map { it.mailboxListState as? MailboxListState.Data }
         .mapNotNull { it?.searchState?.searchQuery }

mail-mailbox/presentation/src/test/kotlin/ch/protonmail/android/mailmailbox/presentation/MailboxViewModelTest.kt

@@ -1706,6 +1706,55 @@ internal class MailboxViewModelTest {
         }
     }
 
+    @Test
+    fun `mailbox pager is not recreated when expanded state of selected folder changes`() = runTest {
+        // Given
+        val folder = MailLabelTestData.buildCustomFolder(
+            id = "folder-1",
+            isExpanded = false,
+            children = listOf("child-1")
+        )
+        val child = MailLabelTestData.buildCustomFolder(id = "child-1", parent = folder)
+        val mailLabelsFlow = MutableStateFlow(
+            MailLabels(
+                system = MailLabelTestData.dynamicSystemLabels,
+                folders = listOf(folder, child),
+                labels = emptyList()
+            )
+        )
+        val currentLocationFlow = MutableStateFlow<MailLabelId>(folder.id)
+        every { observeMailLabels(userId) } returns mailLabelsFlow
+        every { observeLoadedMailLabelId() } returns currentLocationFlow
+        every { observeSelectedMailLabelId() } returns currentLocationFlow
+        coEvery { getSelectedMailLabelId() } returns folder.id
+        every { mailboxReducer.newStateFrom(any(), any()) } returns createMailboxDataState()
+        expectPagerMock(
+            selectedLabelId = folder.id,
+            pagingDataFlow = flowOf(PagingData.from(listOf(unreadMailboxItem)))
+        )
+
+        mailboxViewModel.items.test {
+            awaitItem()
+            verify(exactly = 1) {
+                pagerFactory.create(userId, folder.id, any(), any())
+            }
+
+            // When
+            mailLabelsFlow.value = MailLabels(
+                system = MailLabelTestData.dynamicSystemLabels,
+                folders = listOf(folder.copy(isExpanded = true), child),
+                labels = emptyList()
+            )
+
+            // Then
+            expectNoEvents()
+            verify(exactly = 1) {
+                pagerFactory.create(userId, folder.id, any(), any())
+            }
+            cancelAndIgnoreRemainingEvents()
+        }
+    }
+
     @Test
     fun `mailbox pager is recreated when view mode changes`() = runTest {
         // Given