测试创建自定义字段的Apex类

I have an apex class that creates a custom field on an sObject via an HttpRequest and I'm not sure how to write a test for this because one of the things I need to test is that the field has the correct value, so a mock or a bypass won't work. I can't get enough code coverage for this class if I exclude the web service call. Not sure where to go with this.I have an apex class that creates a custom fiel