[#406] some BirthdayTests fail for MacOS target (#410)

Closes #406

This commits differences how Checkpoints are retrieved from the resource bundle
depending on the target platform.

Sources/ZcashLightClientKit/Constants/WalletBirthday+Constants.swift

@@ -9,11 +9,13 @@ import Foundation
 
 public extension WalletBirthday {
     static func birthday(with height: BlockHeight, network: ZcashNetwork) -> WalletBirthday {
+        let checkpointDirectoryURL = BundleCheckpointURLProvider.default.url(network.networkType)
+
         switch network.networkType {
         case .mainnet:
-      return birthday(with: height, checkpointDirectory: Self.mainnetCheckpointDirectory) ?? .mainnetMin
+            return birthday(with: height, checkpointDirectory: checkpointDirectoryURL) ?? .mainnetMin
         case .testnet:
-      return birthday(with: height, checkpointDirectory: Self.testnetCheckpointDirectory) ?? .testnetMin
+            return birthday(with: height, checkpointDirectory: checkpointDirectoryURL) ?? .testnetMin
         }
     }
 }
@@ -56,3 +58,56 @@ extension WalletBirthday {
         return checkpoint
     }
 }
+
+struct BundleCheckpointURLProvider {
+    var url: (NetworkType) -> URL
+}
+
+
+extension BundleCheckpointURLProvider {
+
+    /// Attempts to resolve the platform by checking `#if os(macOS)` build corresponds to a MacOS target
+    /// `#else` branch of that condition will assume iOS is the target platform
+    static var `default` = BundleCheckpointURLProvider { networkType in
+        #if os(macOS)
+        Self.macOS.url(networkType)
+        #else
+        Self.iOS.url(networkType)
+        #endif
+    }
+
+    static var iOS = BundleCheckpointURLProvider(url: { networkType in
+        switch networkType {
+        case .mainnet:
+            return WalletBirthday.mainnetCheckpointDirectory
+        case .testnet:
+            return WalletBirthday.testnetCheckpointDirectory
+        }
+    })
+
+    /// This variant attempts to retrieve the saplingActivation checkpoint for the given network type
+    /// using `Bundle.module.url(forResource:withExtension:subdirectory:localization)`
+    /// if not found it will return `WalletBirthday.mainnetCheckpointDirectory` or
+    /// `WalletBirthday.testnetCheckpointDirectory`. This responds to tests
+    /// failing on MacOS target because the checkpoint resources would fail.
+    static var macOS = BundleCheckpointURLProvider(url: { networkType in
+        switch networkType {
+        case .mainnet:
+            return Bundle.module.url(
+                forResource: "419200",
+                withExtension: "json",
+                subdirectory: "checkpoints/mainnet/",
+                localization: nil
+            )?
+            .deletingLastPathComponent() ?? WalletBirthday.mainnetCheckpointDirectory
+        case .testnet:
+           return Bundle.module.url(
+                forResource: "280000",
+                withExtension: "json",
+                subdirectory: "checkpoints/testnet/",
+                localization: nil
+            )?
+            .deletingLastPathComponent() ?? WalletBirthday.testnetCheckpointDirectory
+        }
+    })
+}

Sources/ZcashLightClientKit/Constants/WalletBirthday+mainnet.swift

@@ -15,5 +15,4 @@ extension WalletBirthday {
     )
 
     static let mainnetCheckpointDirectory = Bundle.module.bundleURL.appendingPathComponent("checkpoints/mainnet/")
-
 }