[Sasky]

You're trying to reference a function called OnKeyDown() but your function is named BindingTest.OnKeyDown()

Try

<Bindings>
  <Layer name="General">
    <Category name="Test">
      <Action name="TOGGLE_TEST">
        <Down>BindingTest.OnKeyDown()</Down>
      </Action>
    </Category>
  </Layer>
</Bindings>