test.swift

    func refreshDocument(_ documentStruct: DocumentStruct) -> Promises.Promise<Bool> {
        self.documentRequest.fetchDocumentUpdatedAt(documentStruct.uuidString)
            .then(on: self.backgroundQueue) { documentType in
                guard let updatedAt = documentType.updatedAt, updatedAt > documentStruct.updatedAt else {
                    return Promise(false)
                }

                return self.documentRequest.fetchDocument(documentStruct.uuidString)
                    .then { documentType in
                        try self.saveRefreshDocument(documentStruct, documentType)
                        return Promise(true)
                    }
            }.catch(on: self.backgroundQueue) { error in
                if case APIRequestError.notFound = error {
                    try? self.deleteLocalDocumentAndWait(documentStruct)
                }
            }
    }

Better:

    func refreshDocument(_ documentStruct: DocumentStruct) -> Promises.Promise<Bool> {
        self.documentRequest.fetchDocumentUpdatedAt(documentStruct.uuidString)
            .then(on: self.backgroundQueue) { documentType -> Promises.Promise<DocumentAPIType> in
                if let updatedAt = documentType.updatedAt, updatedAt > documentStruct.updatedAt {
                    return self.documentRequest.fetchDocument(documentStruct.uuidString)
                }
                return Promise(documentType)
            }.then(on: self.backgroundQueue) { documentType in
                if let updatedAt = documentType.updatedAt, updatedAt > documentStruct.updatedAt {
                    try self.saveRefreshDocument(documentStruct, documentType)
                }
            }.catch(on: self.backgroundQueue) { error in
                if case APIRequestError.notFound = error {
                    try? self.deleteLocalDocumentAndWait(documentStruct)
                }
            }.then(on: self.backgroundQueue) { documentType in
                return Promise((documentType.updatedAt ?? documentStruct.updatedAt) > documentStruct.updatedAt)
            }
    }