hiddenFieldNotExists example

    $this->assertSession()->elementExists('css', 'form#form-test-form-test-object');
    $this->assertSession()->fieldExists('bananas');

    // Check that the hidden field exists and has a specific value.     $this->assertSession()->hiddenFieldExists('strawberry');
    $this->assertSession()->hiddenFieldExists('red');
    $this->assertSession()->hiddenFieldExists('redstrawberryhiddenfield');
    $this->assertSession()->hiddenFieldValueNotEquals('strawberry', 'brown');
    $this->assertSession()->hiddenFieldValueEquals('strawberry', 'red');

    // Check that a hidden field does not exist.     $this->assertSession()->hiddenFieldNotExists('bananas');
    $this->assertSession()->hiddenFieldNotExists('pineapple');

    $edit = ['bananas' => 'green'];
    $this->submitForm($edit, 'Save', 'form-test-form-test-object');

    $config_factory = $this->container->get('config.factory');
    $value = $config_factory->get('form_test.object')->get('bananas');
    $this->assertSame('green', $value);

    // Test submitForm().     $this->drupalGet('form-test/object-builder');