Implement audio file strategy

Author: jcavar

README.md

@@ -66,7 +66,7 @@ Snapshot audio tests are snapshot tested itself. Please find many examples in: [
 - [x] Add a link to swift snapshot testing
 - [ ] Multi level comparison (first hash, then data, then image)
 - [ ] Use accelerate in downsampling
-- [ ] Add file strategy
+- [x] Add file strategy
 
 ## Contributing
 

Sources/AudioSnapshotTesting/AudioSnapshotTesting.swift

@@ -25,6 +25,45 @@ typealias PlatformColor = UIColor
 typealias PlatformHostingView = _UIHostingView
 #endif
 
+/// Generates a audio file snapshot of the given `AVAudioPCMBuffer.
+extension Snapshotting where Value == AVAudioPCMBuffer, Format == Data {
+    public static func audio() -> Snapshotting<AVAudioPCMBuffer, Data> {
+        return Snapshotting<AVAudioPCMBuffer, Data>(
+            pathExtension: "wav",
+            diffing: Diffing(
+                toData: { $0 },
+                fromData: { $0 },
+                diff: { old, new in
+                    old == new ? nil : ("Audio buffers differ", [])
+                }
+            ),
+            asyncSnapshot: { buffer in
+                Async<Data> { callback in
+                    let tempURL = URL(fileURLWithPath: NSTemporaryDirectory())
+                        .appendingPathComponent(UUID().uuidString)
+                        .appendingPathExtension("wav")
+
+                    do {
+                        let file = try AVAudioFile(forWriting: tempURL, settings: buffer.format.settings)
+                        try file.write(from: buffer)
+                        if #available(iOS 18.0, macOS 15, *) {
+                            file.close()
+                        }
+                        defer {
+                            try? FileManager.default.removeItem(at: tempURL)
+                        }
+
+                        let data = try Data(contentsOf: tempURL)
+                        callback(data)
+                    } catch {
+                        fatalError("Failed to create audio snapshot: \(error)")
+                    }
+                }
+            }
+        )
+    }
+}
+
 @MainActor
 public extension Snapshotting where Format == PlatformImage, Value == (AVAudioPCMBuffer, AVAudioPCMBuffer) {
     /// Generates a overlayed waveform snapshot of the given tuple of `AVAudioPCMBuffer`s.

Tests/AudioSnapshotTestingTests/AudioSnapshotTestingTests.swift

@@ -184,6 +184,21 @@ private func synthesizeSignal(
     return signal
 }
 
+@Test("Audio snapshot of synthesized signal", .snapshots(record: false))
+func audioSnapshotSynthesized() async throws {
+    let signal = synthesizeSignal(
+        frequencyAmplitudePairs: [(440, 0.5), (880, 0.3)],
+        count: 4410
+    )
+    let buffer = createBuffer(from: signal)
+
+    assertSnapshot(
+        of: buffer,
+        as: .audio(),
+        named: "440-880hz"
+    )
+}
+
 private func createBuffer(from samples: [Float]) -> AVAudioPCMBuffer {
     let format = AVAudioFormat(standardFormatWithSampleRate: 32768, channels: 1)!
     let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: AVAudioFrameCount(samples.count))!