testDisposed_PluginAutoDispose() {
    const editableField = new FieldConstructor('testField');
    const plugin = new TestPlugin();

    const noDisposePlugin = new Plugin();
    noDisposePlugin.getTrogClassId = () => 'noDisposeId';
    noDisposePlugin.setAutoDispose(false);

    editableField.registerPlugin(plugin);
    editableField.registerPlugin(noDisposePlugin);
    editableField.dispose();
    assert(editableField.isDisposed());
    assertTrue(plugin.isDisposed());
    assertFalse(noDisposePlugin.isDisposed());
  }
Tests that plugins get auto disposed by default when the field is
disposed. Tests that plugins with setAutoDispose(false) do not get
disposed when the field is disposed.