Add a test suite for post-related methods #39
Description
Add unit tests for the public API related to posts in WFClient:
- getPosts(token:in:completion:)
- movePost(token:postId:with:to:completion:)
- pinPost(token:postId:at:in:completion:)
- unpinPost(token:postId:from:completion:)
- createPost(token:post:in:completion:)
- getPost(token:byId:completion:)
- getPost(token:bySlug:from:completion:)
- updatePost(token:postId:updatedPost:with:completion:)
- deletePost(token:postId:with:completion)
See the developer API docs for useful responses that can be mocked, as in #38.