Form element validation #element_validate not working
It's probably this line:

$form['my_field']['widget']['#element_validate'] = array(array($this, 'myModuleValidateTrue()'));


Which should be this, without parentheses in the method name:

$form['my_field']['widget']['#element_validate'] = array(array($this, 'myModuleValidateTrue'));


See PHP: Callbacks / Callables for the full story.