review: add a test that loads from a render fixture

Sources/SwiftDocC/Model/Rendering/References/ExternalLocationReference.swift

@@ -26,7 +26,7 @@ public struct ExternalLocationReference: RenderReference, URLReference {
 
     public let identifier: RenderReferenceIdentifier
 
-    private let url: String
+    let url: String
 
     enum CodingKeys: String, CodingKey {
         case type

Tests/SwiftDocCTests/Rendering/Rendering Fixtures/external-location-custom-url.json

@@ -0,0 +1,110 @@
+{
+  "schemaVersion" : {
+    "major" : 1,
+    "minor" : 0,
+    "patch" : 0
+  },
+  "seeAlsoSections" : [ ],
+  "metadata" : {
+    "platforms" : [
+      {
+        "name" : "macOS",
+        "introducedAt" : "10.15"
+      }
+    ],
+    "modules" : [
+      { "name" : "MyKit" }
+    ],
+    "title" : "Wifi Access",
+    "roleHeading" : "Plist Key"
+  },
+  "abstract" : [
+    {
+      "type" : "text",
+      "text" : "A "
+    },
+    {
+      "type" : "codeVoice",
+      "code" : "WiFi access"
+    },
+    {
+      "type" : "text",
+      "text" : " abstract description."
+    }
+  ],
+  "sections" : [
+  ],
+  "identifier" : {
+      "url" : "doc:\/\/org.swift.docc.example\/plist\/wifiaccess",
+      "interfaceLanguage": "swift"
+  },
+  "hierarchy" : {
+    "paths" : [["doc:\/\/org.swift.docc.example\/plist\/wifiaccess"]]
+  },
+  "topicSections" : [
+  ],
+  "kind" : "symbol",
+  "references" : {
+    "doc:\/\/org.swift.docc.example\/downloads\/sample.zip": {
+      "identifier": "ExternalLocation.zip",
+      "url": "https://example.com/ExternalLocation.zip",
+      "type": "externalLocation"
+    },
+    "doc:\/\/org.swift.docc.example\/plist\/wifiaccess": {
+      "abstract" : [
+        {
+          "text" : "WiFi access",
+          "type" : "text"
+        }
+      ],
+      "identifier" : "doc:\/\/org.swift.docc.example\/plist\/wifiaccess",
+      "kind" : "symbol",
+      "title" : "WiFi Access",
+      "type" : "topic",
+      "url" : "\/documentation\/mykit"
+    }
+  },
+  "sampleCodeDownload": {
+      "action": {
+          "identifier": "doc:\/\/org.swift.docc.example\/downloads\/sample.zip",
+          "isActive": true,
+          "overridingTitle": "Download",
+          "type": "reference"
+      }
+  },
+  "primaryContentSections" : [
+    {
+      "kind" : "content",
+      "content" : [
+        {
+          "anchor" : "discussion",
+          "level" : 2,
+          "type" : "heading",
+          "text" : "Discussion"
+        },
+        {
+          "type" : "paragraph",
+          "inlineContent" : [
+            {
+              "type" : "text",
+              "text" : "Use "
+            },
+            {
+              "type" : "codeVoice",
+              "code" : "Wifi access"
+            },
+            {
+              "type" : "text",
+              "text" : " to secure wifi access for your app."
+            }
+          ]
+        }
+      ]
+    }
+  ],
+  "variants": [{
+      "paths" : ["\/plist\/wifiaccess"],
+      "traits" : []
+  }]
+}
+

Tests/SwiftDocCTests/Rendering/SampleDownloadTests.swift

@@ -258,4 +258,37 @@ class SampleDownloadTests: XCTestCase {
 
         XCTAssertEqual(baseReference, roundTripReference)
     }
+
+    /// Ensure that an ExternalLocationReference loaded from JSON continues to encode the same
+    /// information after being decoded and re-encoded.
+    func testRoundTripExternalLocationFromFixture() throws {
+        let downloadSymbolURL = Bundle.module.url(
+            forResource: "external-location-custom-url", withExtension: "json",
+            subdirectory: "Rendering Fixtures")!
+
+        let originalData = try Data(contentsOf: downloadSymbolURL)
+        let originalRenderNode = try RenderNode.decode(fromJSON: originalData)
+
+        let encodedRenderNode = try JSONEncoder().encode(originalRenderNode)
+        let symbol = try RenderNode.decode(fromJSON: encodedRenderNode)
+
+        //
+        // Sample Download Details
+        //
+
+        guard let section = symbol.sampleDownload else {
+            XCTFail("Download section not decoded")
+            return
+        }
+
+        guard case RenderInlineContent.reference(let identifier, _, _, _) = section.action else {
+            XCTFail("Could not decode action reference")
+            return
+        }
+
+        XCTAssertEqual(identifier.identifier, "doc://org.swift.docc.example/downloads/sample.zip")
+
+        let externalReference = try XCTUnwrap(symbol.references[identifier.identifier] as? ExternalLocationReference)
+        XCTAssertEqual(externalReference.url, "https://example.com/ExternalLocation.zip")
+    }
 }