code: public MockVpc createVpc(
              final String cidrBlock, final String instanceTenancy) {
  
          MockVpc ret = new MockVpc();
          ret.setCidrBlock(cidrBlock);
          ret.setVpcId("vpc-" + UUID.randomUUID().toString().substring(0, VPC_ID_POSTFIX_LENGTH));
          ret.setInstanceTenancy(instanceTenancy);
          // Make sure only one VPC is default.
          synchronized (this) {
              if (allMockVpcInstances.size() == 0) {
                  ret.setIsDefault(true);
              } else {
                  ret.setIsDefault(false);
                  }
             allMockVpcInstances.put(ret.getVpcId(), ret);
          }
  
         return ret;
       }
docs: Create the mock VPC.
  @param cidrBlock VPC cidr block.
  @param instanceTenancy VPC instance tenancy.
  @return mock VPC.