code: public function assertElementAttribute($selector, $attribute, $expectedValue)
      {
          $actualValue = $this->element('*', $selector)->getAttribute($attribute);
  
          if (null === $actualValue) {
              throw new \InvalidArgumentException(sprintf(
                  'Element does not contain the "%s" attribute.',
                  $attribute
              ));
          } elseif ($actualValue !== $expectedValue) {
              throw new \Exception(sprintf(
                  'Attribute "%s" have the "%s" value which is not equal to "%s".',
                  $attribute,
                  $actualValue,
                  $expectedValue
              ));
          }
      }
docs: @param string $selector
  @param string $attribute
  @param string $expectedValue
  
  @throws \Exception
  
  @example
  Then I should see the "#table_cell" element with "colspan" attribute having "3" value
  
  @Then /^(?:|I )should see the "([^"]*)" element with "([^"]*)" attribute having "([^"]*)" value$/