For limited testing of DialogueTree functionality and progression, the Tree Tester widget provides a quick way to step through any tree and display text. Note that the Tree Tester cannot cutscene-based dialogues.
To use the Tree Tester as an Editor Utility Widget, open the "KPlugins" dropdown toolbar at the top of the main Level Editor window and select "Tree Tester". This will spawn an editor window that can be docked in Unreal Engine's layout. When the game starts, the menu will autopopulate with all DialogueTree Blueprints in the project Content folder. During PIE only, you can drag the tree straight into the level and it will appear on the instance list below. You can then select this tree instance and click "Enter Dialogue" to start stepping through your tree. Spawned trees will NOT be added to the level or persist between sessions.
The Tree Tester is also available as a runtime debug widget. To open it, enter the console command "k.debug". At the top of the screen a debug menu selector will appear. Here, you can select the Tree Tester under "KDialogueSystem" and open it either in the game window by clicking the name or as a popout window by clicking the dark area on the right side.
The Tree Tester will most generally be useful for early testing when the project specific dialogue menus do not exist yet.