FooCacheContext example

  public function testOptimizeTokens(array $context_tokens, array $optimized_context_tokens) {
    $container = $this->getMockBuilder('Drupal\Core\DependencyInjection\Container')
      ->disableOriginalConstructor()
      ->getMock();
    $container->expects($this->any())
      ->method('get')
      ->willReturnMap([
        [
          'cache_context.a',
          Container::EXCEPTION_ON_INVALID_REFERENCE,
          new FooCacheContext(),
        ],
        [
          'cache_context.a.b',
          Container::EXCEPTION_ON_INVALID_REFERENCE,
          new FooCacheContext(),
        ],
        [
          'cache_context.a.b.c',
          Container::EXCEPTION_ON_INVALID_REFERENCE,
          new BazCacheContext(),
        ],
        [