Unit testing with TLF

While unit testing complex formating, I hit several problems. Below are simple tests that fail with an error. Does anybody know what is wrong with these tests?

Thanks for any hints,

Marc

    public function test_apply_Link():void 
    {
        var init:XML = <TextFlow xmlns="http://ns.adobe.com/textLayout/2008"><p><span>aaa</span></p></TextFlow>
        var textFlow:TextFlow = TextConverter.importToFlow(init, TextConverter.TEXT_LAYOUT_FORMAT)
        var editManager:IEditManager = new EditManager()
        textFlow.interactionManager = editManager
        
        editManager.selectRange(1,2)
        editManager.applyLink("http://livedocs.adobe.com/", "_self", true) // throws error:
        /*     
        RangeError: Error #2006: The supplied index is out of bounds.
            at flash.text.engine::GroupElement/replaceElements()
            at flashx.textLayout.elements::ParagraphElement/http://ns.adobe.com/textLayout/internal/2008::insertBlockElement()
            at flashx.textLayout.elements::FlowLeafElement/http://ns.adobe.com/textLayout/internal/2008::createContentElement()
            at flashx.textLayout.elements::SpanElement/http://ns.adobe.com/textLayout/internal/2008::createContentElement()
            at flashx.textLayout.elements::ParagraphElement/http://ns.adobe.com/textLayout/internal/2008::createTextBlock()
            at flashx.textLayout.elements::ParagraphElement/http://ns.adobe.com/textLayout/internal/2008::createContentElement()
            at flashx.textLayout.elements::SubParagraphGroupElement/http://ns.adobe.com/textLayout/internal/2008::setParentAndRelativeStart()
            at flashx.textLayout.elements::LinkElement/http://ns.adobe.com/textLayout/internal/2008::setParentAndRelativeStart()
            at flashx.textLayout.elements::FlowGroupElement/replaceChildren()
            at Function/http://adobe.com/AS3/2006/builtin::apply()
            at flashx.textLayout.elements::ParagraphElement/replaceChildren()
            at flashx.textLayout.edit::TextFlowEdit$/insertNewSPBlock()
            at flashx.textLayout.edit::TextFlowEdit$/makeLink()
            at flashx.textLayout.operations::ApplyLinkOperation/doOperation()
            at flashx.textLayout.edit::EditManager/doInternal()
            at flashx.textLayout.edit::EditManager/doOperation()
            at flashx.textLayout.edit::EditManager/applyLink()
             */
    }

    public function test_undo():void 
    {
        var init:XML = <TextFlow xmlns="http://ns.adobe.com/textLayout/2008"><p><span>aaa</span></p></TextFlow>
        var textFlow:TextFlow = TextConverter.importToFlow(init, TextConverter.TEXT_LAYOUT_FORMAT)
        var undoManager:IUndoManager = new UndoManager()
        var editManager:IEditManager = new EditManager(undoManager)
        textFlow.interactionManager = editManager
        
        editManager.selectRange(1,2)
         var format:TextLayoutFormat = new TextLayoutFormat()
        format.fontWeight = FontWeight.BOLD
        editManager.applyLeafFormat(format)
        
        undoManager.undo() // throws error:
        /*     
        TypeError: Error #1009: Cannot access a property or method of a null object reference
            at flashx.textLayout.edit::EditManager/performUndo()
            at flashx.textLayout.operations::FlowOperation/performUndo()
            at flashx.undo::UndoManager/undo()             
        */
    }