FieldBlock example

'category' => 'Test',
      'admin_label' => 'Test Block',
      'bundles' => ['entity_test'],
      'context_definitions' => [
        'entity' => EntityContextDefinition::fromEntityTypeId('entity_test')->setLabel('Test'),
        'view_mode' => new ContextDefinition('string'),
      ],
    ];
    $formatter_manager = $this->prophesize(FormatterPluginManager::class);
    $module_handler = $this->prophesize(ModuleHandlerInterface::class);

    $block = new FieldBlock(
      $configuration,
      'field_block:entity_test:entity_test:the_field_name',
      $plugin_definition,
      $this->entityFieldManager->reveal(),
      $formatter_manager->reveal(),
      $module_handler->reveal(),
      $this->logger->reveal()
    );
    $block->setContextValue('entity', $entity_prophecy->reveal());
    $block->setContextValue('view_mode', 'default');
    return $block;
  }