Document and test wxItemContainer::Delete() selection handling

Add test checking that selection is reset when deleting the selected
item or any item before, but not after, it.

Also explicitly document this behaviour.

interface/wx/ctrlsub.h

@@ -354,6 +354,12 @@ public:
         failure in debug builds) to remove an item with the index negative or
         greater or equal than the number of items in the control.
 
+        If there is a currently selected item below the item being deleted,
+        i.e. if GetSelection() returns a valid index greater than or equal to
+        @a n, the selection is invalidated when this function is called.
+        However if the selected item appears before the item being deleted, the
+        selection is preserved unchanged.
+
         @param n
             The zero-based item index.
 

tests/controls/itemcontainertest.cpp

@@ -270,6 +270,33 @@ void ItemContainerTestCase::SetString()
 #endif
 }
 
+void ItemContainerTestCase::SelectionAfterDelete()
+{
+    wxItemContainer * const container = GetContainer();
+
+    container->Append("item 0");
+    container->Append("item 1");
+    container->Append("item 2");
+    container->Append("item 3");
+
+    container->SetSelection(1);
+    CHECK( container->GetSelection() == 1 );
+
+    container->Delete(3);
+    CHECK( container->GetSelection() == 1 );
+
+    container->Delete(1);
+    CHECK( container->GetSelection() == wxNOT_FOUND );
+
+    container->SetSelection(1);
+    container->Delete(1);
+    CHECK( container->GetSelection() == wxNOT_FOUND );
+
+    container->SetSelection(0);
+    container->Delete(0);
+    CHECK( container->GetSelection() == wxNOT_FOUND );
+}
+
 void ItemContainerTestCase::SetSelection()
 {
     wxItemContainer * const container = GetContainer();

tests/controls/itemcontainertest.h

@@ -40,6 +40,7 @@ protected:
         CPPUNIT_TEST( Set ); \
         CPPUNIT_TEST( SetSelection ); \
         CPPUNIT_TEST( SetString ); \
+        CPPUNIT_TEST( SelectionAfterDelete ); \
         WXUISIM_TEST( SimSelect );
 
     void Append();
@@ -52,6 +53,7 @@ protected:
     void Set();
     void SetSelection();
     void SetString();
+    void SelectionAfterDelete();
 #if wxUSE_UIACTIONSIMULATOR
     virtual void SimSelect();
 #endif