Renderer.mount: add tests

lua/u/renderer.lua

@@ -60,6 +60,13 @@ function FnComponentContext:update(new_state)
   if self.on_change then vim.schedule(function() self.on_change() end) end
 end
 
+--- @private
+--- @param new_state TState
+function FnComponentContext:update_immediate(new_state)
+  self.state = new_state
+  if self.on_change then self.on_change() end
+end
+
 --- @alias u.renderer.FnComponent<TProps, TState> fun(ctx: u.renderer.FnComponentContext<TProps, TState>): u.renderer.Tree
 
 --- @class u.renderer.Tag