code: public MockInternetGateway attachInternetGateway(final String internetgatewayId,
              final String vpcId) {
          if (internetgatewayId == null) {
              return null;
          }
          MockInternetGateway ret = allMockInternetGateways.get(internetgatewayId);
          if (ret != null) {
              MockInternetGatewayAttachmentType internetGatewayAttachmentType = new MockInternetGatewayAttachmentType();
              internetGatewayAttachmentType.setVpcId(vpcId);
              internetGatewayAttachmentType.setState("Available");
              List<MockInternetGatewayAttachmentType> internetGatewayAttachmentSet
                  = new ArrayList<MockInternetGatewayAttachmentType>();
              internetGatewayAttachmentSet.add(internetGatewayAttachmentType);
              ret.setAttachmentSet(internetGatewayAttachmentSet);
              allMockInternetGateways.put(ret.getInternetGatewayId(), ret);
              }
  
          return ret;
      }
docs: Attach the mock InternetGateway.
  @param vpcId vpc Id for InternetGateway.
  @param internetgatewayId
  internetgatewayId to be deleted
  @return mock InternetGateway.