Update example indentation

Beta/3x

JSONAPI.playground/Pages/Full Client & Server Example.xcplaygroundpage/Contents.swift

@@ -37,7 +37,7 @@ typealias ToManyRelationship<Entity: Relatable> = JSONAPI.ToManyRelationship<Ent
 // JSON:API Documents for this particular API to have Metadata, Links,
 // useful Errors, or an APIDescription (The *SPEC* calls this
 // "API Description" the "JSON:API Object").
-typealias Document<PrimaryResourceBody: JSONAPI.ResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, BasicJSONAPIError<String>>
+typealias Document<PrimaryResourceBody: JSONAPI.CodableResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, BasicJSONAPIError<String>>
 
 // MARK: Entity Definitions
 

JSONAPI.playground/Pages/Usage.xcplaygroundpage/Contents.swift

@@ -64,11 +64,11 @@ if case let .data(bodyData) = peopleResponse.body {
 
 // MARK: - Work in the abstract
 print("-----")
-func process<T: JSONAPIDocument>(document: T) {
-	guard case let .data(body) = document.body else {
+func process<T: CodableJSONAPIDocument>(document: T) {
+    guard let body = document.body.data else {
 		return
 	}
-	let x: T.Body.Data = body
+	let x: T.BodyData = body
 }
 process(document: peopleResponse)
 

JSONAPI.podspec

@@ -16,7 +16,7 @@ Pod::Spec.new do |spec|
   #
 
   spec.name         = "MP-JSONAPI"
-  spec.version      = "2.5.0"
+  spec.version      = "3.0.0"
   spec.summary      = "Swift Codable JSON API framework."
 
   # This description is used to generate tags and improve search results.
@@ -136,6 +136,6 @@ See the JSON API Spec here: https://jsonapi.org/format/
   # spec.requires_arc = true
 
   # spec.xcconfig = { "HEADER_SEARCH_PATHS" => "$(SDKROOT)/usr/include/libxml2" }
-  spec.dependency "Poly", "~> 2.2"
+  spec.dependency "Poly", "~> 2.3.1"
 
 end

Sources/JSONAPI/Document/Document.swift

@@ -408,8 +408,6 @@ extension Document: Decodable, CodableJSONAPIDocument where PrimaryResourceBody:
             throw DocumentDecodingError(error)
         }
 
-        // TODO come back to this and make robust
-
         guard let metaVal = meta else {
             throw JSONAPICodingError.missingOrMalformedMetadata(path: decoder.codingPath)
         }
@@ -494,6 +492,10 @@ extension Document {
         public static func ==(lhs: Document, rhs: ErrorDocument) -> Bool {
             return lhs == rhs.document
         }
+
+        public static func ==(lhs: ErrorDocument, rhs: Document) -> Bool {
+            return lhs.document == rhs
+        }
     }
 
     /// A Document that only supports success bodies. This is useful if you wish to pass around a
@@ -534,7 +536,7 @@ extension Document {
         /// `nil` if the Document is an error response. Otherwise,
         /// a structure containing the primary resource, any included
         /// resources, metadata, and links.
-        var data: BodyData? {
+        public var data: BodyData? {
             return document.body.data
         }
 
@@ -545,7 +547,7 @@ extension Document {
         /// resources dependening on the `PrimaryResourceBody` type.
         ///
         /// See `SingleResourceBody` and `ManyResourceBody`.
-        var primaryResource: PrimaryResourceBody? {
+        public var primaryResource: PrimaryResourceBody? {
             return document.body.primaryResource
         }
 
@@ -553,25 +555,29 @@ extension Document {
         ///
         /// `nil` if the Document is an error document. Otherwise,
         /// zero or more includes.
-        var includes: Includes<IncludeType>? {
+        public var includes: Includes<IncludeType>? {
             return document.body.includes
         }
 
         /// The metadata for the error or data document or `nil` if
         /// no metadata is found.
-        var meta: MetaType? {
+        public var meta: MetaType? {
             return document.body.meta
         }
 
         /// The links for the error or data document or `nil` if
         /// no links are found.
-        var links: LinksType? {
+        public var links: LinksType? {
             return document.body.links
         }
 
         public static func ==(lhs: Document, rhs: SuccessDocument) -> Bool {
             return lhs == rhs.document
         }
+
+        public static func ==(lhs: SuccessDocument, rhs: Document) -> Bool {
+            return lhs.document == rhs
+        }
     }
 }
 

Sources/JSONAPI/Document/DocumentDecodingError.swift

@@ -40,14 +40,12 @@ public enum DocumentDecodingError: Swift.Error, Equatable {
 
     private enum Location: Equatable {
         case data
-        case other
 
-        init(_ context: DecodingError.Context) {
-            if context.codingPath.contains(where: { $0.stringValue == "data" }) {
-                self = .data
-            } else {
-                self = .other
+        init?(_ context: DecodingError.Context) {
+            guard context.codingPath.contains(where: { $0.stringValue == "data" }) else {
+                return nil
             }
+            self = .data
         }
     }
 }

Sources/JSONAPI/Meta/Links.swift

@@ -5,7 +5,7 @@
 //  Created by Mathew Polzin on 11/24/18.
 //
 
-/// A Links structure should contain nothing but JSONAPI.Link properties.
+/// A Links structure should contain nothing but `JSONAPI.Link` properties.
 public protocol Links: Codable, Equatable {}
 
 /// Use NoLinks where no links should belong to a JSON API component

Sources/JSONAPI/Resource/Resource Object/ResourceObject.swift

@@ -414,7 +414,13 @@ public extension ResourceObject {
     init(from decoder: Decoder) throws {
         let container = try decoder.container(keyedBy: ResourceObjectCodingKeys.self)
 
-        let type = try container.decode(String.self, forKey: .type)
+        let type: String
+        do {
+            type = try container.decode(String.self, forKey: .type)
+        } catch let error as DecodingError {
+            throw ResourceObjectDecodingError(error)
+                ?? error
+        }
 
         guard ResourceObject.jsonType == type else {
             throw ResourceObjectDecodingError(

Sources/JSONAPI/Resource/Resource Object/ResourceObjectDecodingError.swift

@@ -102,13 +102,18 @@ public struct ResourceObjectDecodingError: Swift.Error, Equatable {
 extension ResourceObjectDecodingError: CustomStringConvertible {
     public var description: String {
         switch cause {
+        case .keyNotFound where subjectName == ResourceObjectDecodingError.entireObject:
+            return "\(location) object is required and missing."
+        case .keyNotFound where location == .type:
+            return "'type' (a.k.a. JSON:API type name) is required and missing."
         case .keyNotFound:
-            if subjectName == ResourceObjectDecodingError.entireObject {
-                return "\(location) object is required and missing."
-            }
             return "'\(subjectName)' \(location.singular) is required and missing."
+        case .valueNotFound where location == .type:
+            return "'\(location.singular)' (a.k.a. JSON:API type name) is not nullable but null was found."
         case .valueNotFound:
-            return "'\(subjectName)' \(location.singular) is not nullable but null."
+            return "'\(subjectName)' \(location.singular) is not nullable but null was found."
+        case .typeMismatch(expectedTypeName: let expected) where location == .type:
+            return "'\(location.singular)' (a.k.a. the JSON:API type name) is not a \(expected) as expected."
         case .typeMismatch(expectedTypeName: let expected):
             return "'\(subjectName)' \(location.singular) is not a \(expected) as expected."
         case .jsonTypeMismatch(expectedType: let expected, foundType: let found) where location == .type:

Sources/JSONAPI/SparseFields/SparseFieldEncoder.swift

@@ -158,7 +158,7 @@ struct SparseFieldKeyedEncodingContainer<Key, SparseKey>: KeyedEncodingContainer
                                                     forKey key: Key) -> KeyedEncodingContainer<NestedKey> where NestedKey : CodingKey {
         guard shouldAllow(key: key) else {
             return KeyedEncodingContainer(
-                // TODO: not needed by JSONAPI library, but for completeness could
+                // NOTE: not needed by JSONAPI library, but for completeness could
                 //      add an EmptyObjectEncoder that can be returned here so that
                 //      at least nothing gets encoded within the nested container
                 SparseFieldKeyedEncodingContainer<NestedKey, SparseKey>(wrapping: wrappedContainer.nestedContainer(keyedBy: keyType,
@@ -176,7 +176,7 @@ struct SparseFieldKeyedEncodingContainer<Key, SparseKey>: KeyedEncodingContainer
 
     public mutating func nestedUnkeyedContainer(forKey key: Key) -> UnkeyedEncodingContainer {
         guard shouldAllow(key: key) else {
-            // TODO: not needed by JSONAPI library, but for completeness could
+            // NOTE: not needed by JSONAPI library, but for completeness could
             //      add an EmptyObjectEncoder that can be returned here so that
             //      at least nothing gets encoded within the nested container
             return wrappedContainer.nestedUnkeyedContainer(forKey: key)

Sources/JSONAPITesting/Comparisons/ArrayCompare.swift

@@ -14,17 +14,6 @@ public enum ArrayElementComparison: Equatable, CustomStringConvertible {
     case differentValues(String, String)
     case prebuilt(String)
 
-    public init(sameTypeComparison: BasicComparison) {
-        switch sameTypeComparison {
-        case .same:
-            self = .same
-        case .different(let one, let two):
-            self = .differentValues(one, two)
-        case .prebuilt(let str):
-            self = .prebuilt(str)
-        }
-    }
-
     public init(resourceObjectComparison: ResourceObjectComparison) {
         guard !resourceObjectComparison.isSame else {
             self = .same

Sources/JSONAPITesting/Comparisons/AttributesCompare.swift

@@ -1,5 +1,5 @@
 //
-//  File.swift
+//  AttributesCompare.swift
 //  
 //
 //  Created by Mathew Polzin on 11/3/19.
@@ -24,12 +24,16 @@ extension Attributes {
                 continue
             }
 
-            if (attributesEqual(child.value, otherChild.value)) {
-                comparisons[childLabel] = .same
-            } else {
-                let otherChildDescription = attributeDescription(of: otherChild.value)
+            do {
+                if (try attributesEqual(child.value, otherChild.value)) {
+                    comparisons[childLabel] = .same
+                } else {
+                    let otherChildDescription = attributeDescription(of: otherChild.value)
 
-                comparisons[childLabel] = .different(childDescription, otherChildDescription)
+                    comparisons[childLabel] = .different(childDescription, otherChildDescription)
+                }
+            } catch let error {
+                comparisons[childLabel] = .prebuilt(String(describing: error))
             }
         }
 
@@ -37,9 +41,20 @@ extension Attributes {
     }
 }
 
-fileprivate func attributesEqual(_ one: Any, _ two: Any) -> Bool {
+enum AttributeCompareError: Swift.Error, CustomStringConvertible {
+    case nonAttributeTypeProperty(String)
+
+    var description: String {
+        switch self {
+        case .nonAttributeTypeProperty(let type):
+            return "comparison on non-JSON:API Attribute type (\(type)) not supported."
+        }
+    }
+}
+
+fileprivate func attributesEqual(_ one: Any, _ two: Any) throws -> Bool {
     guard let attr = one as? AbstractAttribute else {
-        return false
+        throw AttributeCompareError.nonAttributeTypeProperty(String(describing: type(of: one)))
     }
 
     return attr.equals(two)
@@ -55,6 +70,29 @@ protocol AbstractAttribute {
     func equals(_ other: Any) -> Bool
 }
 
+extension Optional: AbstractAttribute where Wrapped: AbstractAttribute {
+    var abstractDescription: String {
+        switch self {
+        case .none:
+            return "nil"
+        case .some(let rel):
+            return rel.abstractDescription
+        }
+    }
+
+    func equals(_ other: Any) -> Bool {
+        switch self {
+        case .none:
+            return (other as? _AbstractWrapper).map { $0.abstractSelf == nil } ?? false
+        case .some(let rel):
+            guard case let .some(otherVal) = (other as? _AbstractWrapper)?.abstractSelf else {
+                return rel.equals(other)
+            }
+            return rel.equals(otherVal)
+        }
+    }
+}
+
 extension Attribute: AbstractAttribute {
     var abstractDescription: String { String(describing: value) }
 

Sources/JSONAPITesting/Comparisons/DocumentCompare.swift

@@ -33,10 +33,10 @@ public enum BodyComparison: Equatable, CustomStringConvertible {
     case differentErrors(ErrorComparison)
     case differentData(DocumentDataComparison)
 
-    public typealias ErrorComparison = [BasicComparison]
+    public typealias ErrorComparison = [String: BasicComparison]
 
     static func compare<E: JSONAPIError, M: JSONAPI.Meta, L: JSONAPI.Links>(errors errors1: [E], _ meta1: M?, _ links1: L?, with errors2: [E], _ meta2: M?, _ links2: L?) -> ErrorComparison {
-        return errors1.compare(
+        let errorComparisons = errors1.compare(
             to: errors2,
             using: { error1, error2 in
                 guard error1 != error2 else {
@@ -48,9 +48,19 @@ public enum BodyComparison: Equatable, CustomStringConvertible {
                     String(describing: error2)
                 )
             }
-        ).map(BasicComparison.init) + [
-            BasicComparison(meta1, meta2),
-            BasicComparison(links1, links2)
+        ).map(BasicComparison.init)
+            .filter { !$0.isSame }
+            .map { $0.rawValue }
+            .joined(separator: ", ")
+
+        let errorComparisonString = errorComparisons.isEmpty
+            ? nil
+            : errorComparisons
+
+        return [
+            "Errors": errorComparisonString.map { BasicComparison.prebuilt("(\($0))") } ?? .same,
+            "Metadata": BasicComparison(meta1, meta2),
+            "Links": BasicComparison(links1, links2)
         ]
     }
 
@@ -67,8 +77,8 @@ public enum BodyComparison: Equatable, CustomStringConvertible {
             return "\(left) ≠ \(right)"
         case .differentErrors(let comparisons):
             return comparisons
-                .filter { !$0.isSame }
-                .map { $0.rawValue }
+                .filter { !$0.value.isSame }
+                .map { "\($0.key): \($0.value.rawValue)" }
                 .sorted()
                 .joined(separator: ", ")
         case .differentData(let comparison):
@@ -104,7 +114,7 @@ extension DocumentBody where Self: Equatable, PrimaryResourceBody: TestableResou
             return .differentErrors(
                 BodyComparison.compare(
                     errors: errors1, meta, links,
-                    with: errors2, meta, links
+                    with: errors2, other.meta, other.links
                 )
             )
         }

Sources/JSONAPITesting/Comparisons/Optional+AbstractWrapper.swift

@@ -0,0 +1,16 @@
+//
+//  Optional+AbstractWrapper.swift
+//  JSONAPITesting
+//
+//  Created by Mathew Polzin on 11/15/19.
+//
+
+protocol _AbstractWrapper {
+    var abstractSelf: Any? { get }
+}
+
+extension Optional: _AbstractWrapper {
+    var abstractSelf: Any? {
+        return self
+    }
+}

Sources/JSONAPITesting/Comparisons/RelationshipsCompare.swift

@@ -1,5 +1,5 @@
 //
-//  File.swift
+//  RelationshipsCompare.swift
 //  
 //
 //  Created by Mathew Polzin on 11/3/19.
@@ -24,12 +24,16 @@ extension Relationships {
                 continue
             }
 
-            if (relationshipsEqual(child.value, otherChild.value)) {
-                comparisons[childLabel] = .same
-            } else {
-                let otherChildDescription = relationshipDescription(of: otherChild.value)
+            do {
+                if (try relationshipsEqual(child.value, otherChild.value)) {
+                    comparisons[childLabel] = .same
+                } else {
+                    let otherChildDescription = relationshipDescription(of: otherChild.value)
 
-                comparisons[childLabel] = .different(childDescription, otherChildDescription)
+                    comparisons[childLabel] = .different(childDescription, otherChildDescription)
+                }
+            } catch let error {
+                comparisons[childLabel] = .prebuilt(String(describing: error))
             }
         }
 
@@ -37,9 +41,20 @@ extension Relationships {
     }
 }
 
-fileprivate func relationshipsEqual(_ one: Any, _ two: Any) -> Bool {
+enum RelationshipCompareError: Swift.Error, CustomStringConvertible {
+    case nonRelationshipTypeProperty(String)
+
+    var description: String {
+        switch self {
+        case .nonRelationshipTypeProperty(let type):
+            return "comparison on non-JSON:API Relationship type (\(type)) not supported."
+        }
+    }
+}
+
+fileprivate func relationshipsEqual(_ one: Any, _ two: Any) throws -> Bool {
     guard let attr = one as? AbstractRelationship else {
-        return false
+        throw RelationshipCompareError.nonRelationshipTypeProperty(String(describing: type(of: one)))
     }
 
     return attr.equals(two)
@@ -55,6 +70,29 @@ protocol AbstractRelationship {
     func equals(_ other: Any) -> Bool
 }
 
+extension Optional: AbstractRelationship where Wrapped: AbstractRelationship {
+    var abstractDescription: String {
+        switch self {
+        case .none:
+            return "nil"
+        case .some(let rel):
+            return rel.abstractDescription
+        }
+    }
+
+    func equals(_ other: Any) -> Bool {
+        switch self {
+        case .none:
+            return (other as? _AbstractWrapper).map { $0.abstractSelf == nil } ?? false
+        case .some(let rel):
+            guard case let .some(otherVal) = (other as? _AbstractWrapper)?.abstractSelf else {
+                return rel.equals(other)
+            }
+            return rel.equals(otherVal)
+        }
+    }
+}
+
 extension ToOneRelationship: AbstractRelationship {
     var abstractDescription: String {
         if meta is NoMetadata && links is NoLinks {

Tests/JSONAPITestingTests/Comparisons/ArrayCompareTests.swift

@@ -0,0 +1,86 @@
+//
+//  ArrayCompareTests.swift
+//  JSONAPITestingTests
+//
+//  Created by Mathew Polzin on 11/14/19.
+//
+
+import XCTest
+@testable import JSONAPITesting
+
+final class ArrayCompareTests: XCTestCase {
+    func test_same() {
+        let arr1 = ["a", "b", "c"]
+        let arr2 = ["a", "b", "c"]
+
+        let comparison = arr1.compare(to: arr2) { str1, str2 in
+            str1 == str2 ? .same : .differentValues(str1, str2)
+        }
+
+        XCTAssertEqual(
+            comparison,
+            [.same, .same, .same]
+        )
+
+        XCTAssertEqual(comparison.map { $0.description }, ["same", "same", "same"])
+
+        XCTAssertEqual(comparison.map(BasicComparison.init(reducing:)), [.same, .same, .same])
+
+        XCTAssertEqual(comparison.map(BasicComparison.init(reducing:)).map { $0.description }, ["same", "same", "same"])
+    }
+
+    func test_differentLengths() {
+        let arr1 = ["a", "b", "c"]
+        let arr2 = ["a", "b"]
+
+        let comparison1 = arr1.compare(to: arr2) { str1, str2 in
+            str1 == str2 ? .same : .differentValues(str1, str2)
+        }
+
+        XCTAssertEqual(
+            comparison1,
+            [.same, .same, .missing]
+        )
+
+        XCTAssertEqual(comparison1.map { $0.description }, ["same", "same", "missing"])
+
+        XCTAssertEqual(comparison1.map(BasicComparison.init(reducing:)), [.same, .same, .different("array length 1", "array length 2")])
+
+        let comparison2 = arr2.compare(to: arr1) { str1, str2 in
+            str1 == str2 ? .same : .differentValues(str1, str2)
+        }
+
+        XCTAssertEqual(
+            comparison2,
+            [.same, .same, .missing]
+        )
+
+        XCTAssertEqual(comparison2.map { $0.description }, ["same", "same", "missing"])
+
+        XCTAssertEqual(comparison2.map(BasicComparison.init(reducing:)), [.same, .same, .different("array length 1", "array length 2")])
+    }
+
+    func test_differentValues() {
+        let arr1 = ["c", "b", "a"]
+        let arr2 = ["a", "b", "c"]
+
+        let comparison = arr1.compare(to: arr2) { str1, str2 in
+            str1 == str2 ? .same : .differentValues(str1, str2)
+        }
+
+        XCTAssertEqual(
+            comparison,
+            [.differentValues("c", "a"), .same, .differentValues("a", "c")]
+        )
+
+        XCTAssertEqual(comparison.map { $0.description }, ["c ≠ a", "same", "a ≠ c"])
+    }
+
+    func test_reducePrebuilt() {
+        let prebuilt = ArrayElementComparison.prebuilt("hello world")
+
+        XCTAssertEqual(BasicComparison(reducing: prebuilt), .prebuilt("hello world"))
+
+        XCTAssertEqual(BasicComparison(reducing: prebuilt).description, "hello world")
+    }
+}

Tests/JSONAPITestingTests/Comparisons/AttributesCompareTests.swift

@@ -1,5 +1,5 @@
 //
-//  File.swift
+//  AttributesCompareTests.swift
 //  
 //
 //  Created by Mathew Polzin on 11/3/19.
@@ -10,13 +10,16 @@ import JSONAPI
 import JSONAPITesting
 
 final class AttributesCompareTests: XCTestCase {
-    func test_sameAttributes() {
+    func test_sameAttributes() throws {
         let attr1 = TestAttributes(
             string: "hello world",
             int: 10,
             bool: true,
             double: 105.4,
-            struct: .init(value: .init())
+            struct: .init(value: .init()),
+            transformed: try .init(rawValue: 10),
+            optional: .init(value: 20),
+            optionalTransformed: try .init(rawValue: 10)
         )
         let attr2 = attr1
 
@@ -25,24 +28,33 @@ final class AttributesCompareTests: XCTestCase {
             "int": .same,
             "bool": .same,
             "double": .same,
-            "struct": .same
+            "struct": .same,
+            "transformed": .same,
+            "optional": .same,
+            "optionalTransformed": .same
         ])
     }
 
-    func test_differentAttributes() {
+    func test_differentAttributes() throws {
         let attr1 = TestAttributes(
             string: "hello world",
             int: 10,
             bool: true,
             double: 105.4,
-            struct: .init(value: .init())
+            struct: .init(value: .init()),
+            transformed: try .init(rawValue: 10),
+            optional: nil,
+            optionalTransformed: nil
         )
         let attr2 = TestAttributes(
             string: "hello",
             int: 11,
             bool: false,
             double: 1.4,
-            struct: .init(value: .init(val: "there"))
+            struct: .init(value: .init(val: "there")),
+            transformed: try .init(rawValue: 11),
+            optional: .init(value: 20.5),
+            optionalTransformed: try .init(rawValue: 10)
         )
 
         XCTAssertEqual(attr1.compare(to: attr2), [
@@ -50,7 +62,30 @@ final class AttributesCompareTests: XCTestCase {
             "int": .different("10", "11"),
             "bool": .different("true", "false"),
             "double": .different("105.4", "1.4"),
-            "struct": .different("string: hello", "string: there")
+            "struct": .different("string: hello", "string: there"),
+            "transformed": .different("10", "11"),
+            "optional": .different("nil", "20.5"),
+            "optionalTransformed": .different("nil", "10")
+        ])
+    }
+
+    func test_nonAttributeTypes() {
+        let attr1 = NonAttributeTest(
+            string: "hello",
+            int: 10,
+            double: 11.2,
+            bool: true,
+            struct: .init(),
+            optional: nil
+        )
+
+        XCTAssertEqual(attr1.compare(to: attr1), [
+            "string": .prebuilt("comparison on non-JSON:API Attribute type (String) not supported."),
+            "int": .prebuilt("comparison on non-JSON:API Attribute type (Int) not supported."),
+            "double": .prebuilt("comparison on non-JSON:API Attribute type (Double) not supported."),
+            "bool": .prebuilt("comparison on non-JSON:API Attribute type (Bool) not supported."),
+            "struct": .prebuilt("comparison on non-JSON:API Attribute type (Struct) not supported."),
+            "optional": .prebuilt("comparison on non-JSON:API Attribute type (Optional<Int>) not supported.")
         ])
     }
 }
@@ -61,14 +96,32 @@ private struct TestAttributes: JSONAPI.Attributes {
     let bool: Attribute<Bool>
     let double: Attribute<Double>
     let `struct`: Attribute<Struct>
+    let transformed: TransformedAttribute<Int, TestTransformer>
+    let optional: Attribute<Double>?
+    let optionalTransformed: TransformedAttribute<Int, TestTransformer>?
+}
 
-    struct Struct: Equatable, Codable, CustomStringConvertible {
-        let string: String
+private struct Struct: Equatable, Codable, CustomStringConvertible {
+    let string: String
 
-        init(val: String = "hello") {
-            self.string = val
-        }
+    init(val: String = "hello") {
+        self.string = val
+    }
 
-        var description: String { return "string: \(string)" }
+    var description: String { return "string: \(string)" }
+}
+
+private enum TestTransformer: Transformer {
+    static func transform(_ value: Int) throws -> String {
+        return "\(value)"
     }
 }
+
+private struct NonAttributeTest: JSONAPI.Attributes {
+    let string: String
+    let int: Int
+    let double: Double
+    let bool: Bool
+    let `struct`: Struct
+    let optional: Int?
+}

Tests/JSONAPITestingTests/Comparisons/DocumentCompareTests.swift

@@ -21,6 +21,8 @@ final class DocumentCompareTests: XCTestCase {
         XCTAssertTrue(d8.compare(to: d8).differences.isEmpty)
         XCTAssertTrue(d9.compare(to: d9).differences.isEmpty)
         XCTAssertTrue(d10.compare(to: d10).differences.isEmpty)
+
+        XCTAssertEqual(String(describing: d1.compare(to: d1).body), "same")
     }
 
     func test_errorAndData() {
@@ -34,8 +36,33 @@ final class DocumentCompareTests: XCTestCase {
     }
 
     func test_differentErrors() {
-        XCTAssertEqual(d2.compare(to: d4).differences, [
-            "Body": "status: 500, title: Internal Error ≠ status: 404, title: Not Found"
+        let comparison = d2.compare(to: d4)
+        XCTAssertEqual(comparison.differences, [
+            "Body": "Errors: (status: 500, title: Internal Error ≠ status: 404, title: Not Found)"
+        ])
+
+        XCTAssertEqual(String(describing: comparison), "(Body: Errors: (status: 500, title: Internal Error ≠ status: 404, title: Not Found))")
+    }
+
+    func test_sameErrorsDifferentMetadata() {
+        let errors = [
+        BasicJSONAPIError<String>.error(.init(id: nil, status: "500", title: "Internal Error"))
+        ]
+        let doc1 = SingleDocumentWithMetaAndLinks(
+            apiDescription: TestAPIDescription(version: "1", meta: .none),
+            errors: errors,
+            meta: nil,
+            links: nil
+        )
+        let doc2 = SingleDocumentWithMetaAndLinks(
+            apiDescription: TestAPIDescription(version: "1", meta: .none),
+            errors: errors,
+            meta: .init(total: 11),
+            links: nil
+        )
+
+        XCTAssertEqual(doc1.compare(to: doc2).differences, [
+            "Body": "Metadata: nil ≠ Optional(total: 11)"
         ])
     }
 
@@ -60,6 +87,24 @@ final class DocumentCompareTests: XCTestCase {
             "Body": ##"(Primary Resource: (resource 1: 'age' attribute: 10 ≠ 12, 'bestFriend' relationship: Optional(Id(2)) ≠ nil, 'favoriteColor' attribute: nil ≠ Optional("blue"), 'name' attribute: name ≠ Fig, id: 1 ≠ 5))"##
         ])
     }
+
+    func test_differentMetadata() {
+        XCTAssertEqual(d11.compare(to: d12).differences, [
+            "Body": "(Meta: total: 10 ≠ total: 10000)"
+        ])
+    }
+
+    func test_differentLinks() {
+        XCTAssertEqual(d11.compare(to: d13).differences, [
+            "Body": ##"(Links: TestLinks(link: JSONAPI.Link<Swift.String, JSONAPI.NoMetadata>(url: "http://google.com", meta: No Metadata)) ≠ TestLinks(link: JSONAPI.Link<Swift.String, JSONAPI.NoMetadata>(url: "http://yahoo.com", meta: No Metadata)))"##
+        ])
+    }
+
+    func test_differentAPIDescription() {
+        XCTAssertEqual(d11.compare(to: d14).differences, [
+            "API Description": ##"APIDescription<NoMetadata>(version: "10", meta: No Metadata) ≠ APIDescription<NoMetadata>(version: "1", meta: No Metadata)"##
+        ])
+    }
 }
 
 fileprivate enum TestDescription: JSONAPI.ResourceObjectDescription {
@@ -98,6 +143,22 @@ fileprivate typealias TestType2 = ResourceObject<TestDescription2, NoMetadata, N
 
 fileprivate typealias SingleDocument = JSONAPI.Document<SingleResourceBody<TestType>, NoMetadata, NoLinks, Include2<TestType, TestType2>, NoAPIDescription, BasicJSONAPIError<String>>
 
+fileprivate struct TestMetadata: JSONAPI.Meta, CustomStringConvertible {
+    let total: Int
+
+    var description: String {
+        "total: \(total)"
+    }
+}
+
+fileprivate struct TestLinks: JSONAPI.Links {
+    let link: Link<String, NoMetadata>
+}
+
+typealias TestAPIDescription = APIDescription<NoMetadata>
+
+fileprivate typealias SingleDocumentWithMetaAndLinks = JSONAPI.Document<SingleResourceBody<TestType>, TestMetadata, TestLinks, Include2<TestType, TestType2>, TestAPIDescription, BasicJSONAPIError<String>>
+
 fileprivate typealias OptionalSingleDocument = JSONAPI.Document<SingleResourceBody<TestType?>, NoMetadata, NoLinks, Include2<TestType, TestType2>, NoAPIDescription, BasicJSONAPIError<String>>
 
 fileprivate typealias ManyDocument = JSONAPI.Document<ManyResourceBody<TestType>, NoMetadata, NoLinks, Include2<TestType, TestType2>, NoAPIDescription, BasicJSONAPIError<String>>
@@ -220,3 +281,35 @@ fileprivate let d10 = SingleDocument(
     meta: .none,
     links: .none
 )
+
+fileprivate let d11 = SingleDocumentWithMetaAndLinks(
+    apiDescription: TestAPIDescription(version: "10", meta: .none),
+    body: .init(resourceObject: r2),
+    includes: .none,
+    meta: TestMetadata(total: 10),
+    links: TestLinks(link: .init(url: "http://google.com"))
+)
+
+fileprivate let d12 = SingleDocumentWithMetaAndLinks(
+    apiDescription: TestAPIDescription(version: "10", meta: .none),
+    body: .init(resourceObject: r2),
+    includes: .none,
+    meta: TestMetadata(total: 10000),
+    links: TestLinks(link: .init(url: "http://google.com"))
+)
+
+fileprivate let d13 = SingleDocumentWithMetaAndLinks(
+    apiDescription: TestAPIDescription(version: "10", meta: .none),
+    body: .init(resourceObject: r2),
+    includes: .none,
+    meta: TestMetadata(total: 10),
+    links: TestLinks(link: .init(url: "http://yahoo.com"))
+)
+
+fileprivate let d14 = SingleDocumentWithMetaAndLinks(
+    apiDescription: TestAPIDescription(version: "1", meta: .none),
+    body: .init(resourceObject: r2),
+    includes: .none,
+    meta: TestMetadata(total: 10),
+    links: TestLinks(link: .init(url: "http://google.com"))
+)

Tests/JSONAPITestingTests/Comparisons/RelationshipsCompareTests.swift

@@ -1,5 +1,5 @@
 //
-//  File.swift
+//  RelationshipCompareTests.swift
 //  
 //
 //  Created by Mathew Polzin on 11/5/19.
@@ -10,5 +10,176 @@ import JSONAPI
 import JSONAPITesting
 
 final class RelationshipsCompareTests: XCTestCase {
-    // TODO: write tests
+    func test_same() {
+        let r1 = TestRelationships(
+            a: t1,
+            b: t2,
+            c: t3,
+            d: t4
+        )
+        let r2 = r1
+
+        XCTAssertTrue(r1.compare(to: r2).allSatisfy { $0.value == .same })
+
+        let r3 = TestRelationships(
+            a: t1_differentId,
+            b: t2_differentLinks,
+            c: t3_differentId,
+            d: t4_differentLinks
+        )
+        let r4 = r3
+
+        XCTAssertTrue(r3.compare(to: r4).allSatisfy { $0.value == .same })
+
+        let r5 = TestRelationships(
+            a: nil,
+            b: nil,
+            c: nil,
+            d: nil
+        )
+        let r6 = r5
+
+        XCTAssertTrue(r5.compare(to: r6).allSatisfy { $0.value == .same })
+    }
+
+    func test_differentIds() {
+        let r1 = TestRelationships(
+            a: t1,
+            b: nil,
+            c: t3,
+            d: nil
+        )
+
+        let r2 = TestRelationships(
+            a: t1_differentId,
+            b: nil,
+            c: t3_differentId,
+            d: nil
+        )
+
+        XCTAssertEqual(r1.compare(to: r2), [
+            "a": .different("Id(123)", "Id(999)"),
+            "b": .same,
+            "c": .different("123, 456", "999, 1010"),
+            "d": .same
+        ])
+    }
+
+    func test_differentMetadata() {
+        let r1 = TestRelationships(
+            a: nil,
+            b: t2,
+            c: nil,
+            d: t4
+        )
+
+        let r2 = TestRelationships(
+            a: nil,
+            b: t2_differentMeta,
+            c: nil,
+            d: t4_differentMeta
+        )
+
+        XCTAssertEqual(r1.compare(to: r2), [
+            "a": .same,
+            "b": .different(#"("Id(456)", "hello: world", "link: http://google.com")"#, #"("Id(456)", "hello: there", "link: http://google.com")"#),
+            "c": .same,
+            "d": .different(#"("123, 456", "hello: world", "link: http://google.com")"#, #"("123, 456", "hello: there", "link: http://google.com")"#)
+        ])
+    }
+
+    func test_differentLinks() {
+        let r1 = TestRelationships(
+            a: nil,
+            b: t2,
+            c: nil,
+            d: t4
+        )
+
+        let r2 = TestRelationships(
+            a: nil,
+            b: t2_differentLinks,
+            c: nil,
+            d: t4_differentLinks
+        )
+
+        XCTAssertEqual(r1.compare(to: r2), [
+            "a": .same,
+            "b": .different(#"("Id(456)", "hello: world", "link: http://google.com")"#, #"("Id(456)", "hello: world", "link: http://yahoo.com")"#),
+            "c": .same,
+            "d": .different(#"("123, 456", "hello: world", "link: http://google.com")"#, #"("123, 456", "hello: world", "link: http://yahoo.com")"#)
+        ])
+    }
+
+    func test_nonRelationshipTypes() {
+        let r1 = TestNonRelationships(
+            a: .init(attributes: .none, relationships: .none, meta: .none, links: .none),
+            b: false,
+            c: 10,
+            d: "1234"
+        )
+
+        XCTAssertEqual(r1.compare(to: r1), [
+            "a": .prebuilt("comparison on non-JSON:API Relationship type (ResourceObject<TestTypeDescription, NoMetadata, NoLinks, String>) not supported."),
+            "b": .prebuilt("comparison on non-JSON:API Relationship type (Bool) not supported."),
+            "c": .prebuilt("comparison on non-JSON:API Relationship type (Int) not supported."),
+            "d": .prebuilt("comparison on non-JSON:API Relationship type (Id<String, ResourceObject<TestTypeDescription, NoMetadata, NoLinks, String>>) not supported.")
+        ])
+    }
+
+    let t1 = ToOneRelationship<TestType, NoMetadata, NoLinks>(id: "123")
+    let t2 = ToOneRelationship<TestType, TestMeta, TestLinks>(id: "456", meta: .init(hello: "world"), links: .init(link: .init(url: "http://google.com")))
+    let t3 = ToManyRelationship<TestType, NoMetadata, NoLinks>(ids: ["123", "456"])
+    let t4 = ToManyRelationship<TestType, TestMeta, TestLinks>(ids: ["123", "456"], meta: .init(hello: "world"), links: .init(link: .init(url: "http://google.com")))
+
+    let t1_differentId = ToOneRelationship<TestType, NoMetadata, NoLinks>(id: "999")
+    let t3_differentId = ToManyRelationship<TestType, NoMetadata, NoLinks>(ids: ["999", "1010"])
+
+    let t2_differentLinks = ToOneRelationship<TestType, TestMeta, TestLinks>(id: "456", meta: .init(hello: "world"), links: .init(link: .init(url: "http://yahoo.com")))
+    let t4_differentLinks = ToManyRelationship<TestType, TestMeta, TestLinks>(ids: ["123", "456"], meta: .init(hello: "world"), links: .init(link: .init(url: "http://yahoo.com")))
+
+    let t2_differentMeta = ToOneRelationship<TestType, TestMeta, TestLinks>(id: "456", meta: .init(hello: "there"), links: .init(link: .init(url: "http://google.com")))
+    let t4_differentMeta = ToManyRelationship<TestType, TestMeta, TestLinks>(ids: ["123", "456"], meta: .init(hello: "there"), links: .init(link: .init(url: "http://google.com")))
+}
+
+// MARK: - Test Types
+extension RelationshipsCompareTests {
+    enum TestTypeDescription: ResourceObjectDescription {
+        static let jsonType: String = "test"
+
+        typealias Attributes = NoAttributes
+        typealias Relationships = NoRelationships
+    }
+
+    typealias TestType = ResourceObject<TestTypeDescription, NoMetadata, NoLinks, String>
+
+    struct TestMeta: JSONAPI.Meta, CustomDebugStringConvertible {
+        let hello: String
+
+        var debugDescription: String {
+            "hello: \(hello)"
+        }
+    }
+
+    struct TestLinks: JSONAPI.Links, CustomDebugStringConvertible {
+        let link: Link<String, NoMetadata>
+
+        var debugDescription: String {
+            "link: \(link.url)"
+        }
+    }
+
+    struct TestRelationships: JSONAPI.Relationships {
+        let a: ToOneRelationship<TestType, NoMetadata, NoLinks>?
+        let b: ToOneRelationship<TestType, TestMeta, TestLinks>?
+        let c: ToManyRelationship<TestType, NoMetadata, NoLinks>?
+        let d: ToManyRelationship<TestType, TestMeta, TestLinks>?
+    }
+
+    struct TestNonRelationships: JSONAPI.Relationships {
+        let a: TestType
+        let b: Bool
+        let c: Int
+        let d: JSONAPI.Id<String, TestType>
+    }
 }

Tests/JSONAPITestingTests/Comparisons/ResourceObjectCompareTests.swift

@@ -1,5 +1,5 @@
 //
-//  File.swift
+//  ResourceObjectCompareTests.swift
 //  
 //
 //  Created by Mathew Polzin on 11/3/19.
@@ -11,14 +11,72 @@ import JSONAPITesting
 
 final class ResourceObjectCompareTests: XCTestCase {
     func test_same() {
-        print(test1.compare(to: test1).differences)
         XCTAssertTrue(test1.compare(to: test1).differences.isEmpty)
-        XCTAssertTrue(test2.compare(to: test2).differences.isEmpty)
+        XCTAssertTrue(test1_differentId.compare(to: test1_differentId).differences.isEmpty)
+        XCTAssertTrue(test1_differentAttributes.compare(to: test1_differentAttributes).differences.isEmpty)
     }
 
-    func test_different() {
-        // TODO: write actual test
-        print(test1.compare(to: test2).differences.map { "\($0): \($1)" }.joined(separator: ", "))
+    func test_differentAttributes() {
+        XCTAssertEqual(test1.compare(to: test1_differentAttributes).differences, [
+            "'favoriteColor' attribute": #"Optional("red") ≠ nil"#,
+            "'name' attribute": "James ≠ Fred",
+            "'age' attribute": "12 ≠ 10"
+        ])
+    }
+
+    func test_differentRelationships() {
+        XCTAssertEqual(test1.compare(to: test1_differentRelationships).differences, [
+            "'parents' relationship": "4, 5 ≠ 3",
+            "'bestFriend' relationship": "Optional(Id(3)) ≠ nil"
+        ])
+    }
+
+    func test_differentIds() {
+        XCTAssertEqual(test1.compare(to: test1_differentId).differences, [
+            "id": "2 ≠ 3"
+        ])
+    }
+
+    func test_differentMetadata() {
+        let test1 = TestType2(
+            id: "2",
+            attributes: .none,
+            relationships: .none,
+            meta: .init(total: 10),
+            links: .init(link: .init(url: "http://google.com"))
+        )
+        let test1_differentMeta = TestType2(
+            id: "2",
+            attributes: .none,
+            relationships: .none,
+            meta: .init(total: 12),
+            links: .init(link: .init(url: "http://google.com"))
+        )
+
+        XCTAssertEqual(test1.compare(to: test1_differentMeta).differences, [
+            "meta": "total: 10 ≠ total: 12"
+        ])
+    }
+
+    func test_differentLinks() {
+        let test1 = TestType2(
+            id: "2",
+            attributes: .none,
+            relationships: .none,
+            meta: .init(total: 10),
+            links: .init(link: .init(url: "http://google.com"))
+        )
+        let test1_differentLinks = TestType2(
+            id: "2",
+            attributes: .none,
+            relationships: .none,
+            meta: .init(total: 10),
+            links: .init(link: .init(url: "http://yahoo.com"))
+        )
+
+        XCTAssertEqual(test1.compare(to: test1_differentLinks).differences, [
+            "links": "link: http://google.com ≠ link: http://yahoo.com"
+        ])
     }
 
     fileprivate let test1 = TestType(
@@ -35,15 +93,43 @@ final class ResourceObjectCompareTests: XCTestCase {
         links: .none
     )
 
-    fileprivate let test2 = TestType(
+    fileprivate let test1_differentId = TestType(
         id: "3",
+        attributes: .init(
+            name: "James",
+            age: 12,
+            favoriteColor: "red"),
+        relationships: .init(
+            bestFriend: "3",
+            parents: ["4", "5"]
+        ),
+        meta: .none,
+        links: .none
+    )
+
+    fileprivate let test1_differentAttributes = TestType(
+        id: "2",
         attributes: .init(
             name: "Fred",
             age: 10,
             favoriteColor: .init(value: nil)),
+        relationships: .init(
+            bestFriend: "3",
+            parents: ["4", "5"]
+        ),
+        meta: .none,
+        links: .none
+    )
+
+    fileprivate let test1_differentRelationships = TestType(
+        id: "2",
+        attributes: .init(
+            name: "James",
+            age: 12,
+            favoriteColor: "red"),
         relationships: .init(
             bestFriend: nil,
-            parents: ["1"]
+            parents: ["3"]
         ),
         meta: .none,
         links: .none
@@ -66,3 +152,29 @@ private enum TestDescription: JSONAPI.ResourceObjectDescription {
 }
 
 private typealias TestType = ResourceObject<TestDescription, NoMetadata, NoLinks, String>
+
+private struct TestMetadata: JSONAPI.Meta, CustomStringConvertible {
+    let total: Int
+
+    var description: String {
+        "total: \(total)"
+    }
+}
+
+private struct TestLinks: JSONAPI.Links, CustomStringConvertible {
+    let link: Link<String, NoMetadata>
+
+    var description: String {
+        "link: \(link.url)"
+    }
+}
+
+private enum TestDescription2: JSONAPI.ResourceObjectDescription {
+    static let jsonType: String = "test_type2"
+
+    typealias Attributes = NoAttributes
+
+    typealias Relationships = NoRelationships
+}
+
+private typealias TestType2 = ResourceObject<TestDescription2, TestMetadata, TestLinks, String>