code: public function assertTextualField($selector, $not, $expected)
      {
          (new FormValueAssertion($this, $selector, $not, $expected))->textual();
      }
docs: @example
  And check that "Users" field has "admin" value
  And check that "Users" field has not "customer" value
  
  @Then /^(?:|I )check that "([^"]*)" field has(| not) "([^"]*)" value$/