Feat/build library dylib script

Package.swift

@@ -17,8 +17,12 @@ let package = Package(
     ],
     targets: [
         .binaryTarget(
-            name: "_Differentiation", 
+            name: "_Differentiation",
             path: "_Differentiation.xcframework"
-        )
+        ),
+        .testTarget(
+            name: "DifferentiationTests",
+            dependencies: ["_Differentiation"]
+        ),
     ]
 )

Tests/DifferentiationTests/DifferentiationTests.swift

@@ -0,0 +1,58 @@
+import XCTest
+import _Differentiation
+
+@differentiable(reverse)
+private func quadratic(_ x: Double) -> Double {
+    x * x + 3 * x + 2
+}
+
+@differentiable(reverse)
+private func weightedPolynomial(_ x: Double, _ y: Double) -> Double {
+    x * x + x * y + y
+}
+
+private struct Scalar: Differentiable, AdditiveArithmetic {
+    var value: Double
+
+    static let zero = Scalar(value: 0)
+
+    static func + (lhs: Scalar, rhs: Scalar) -> Scalar {
+        Scalar(value: lhs.value + rhs.value)
+    }
+
+    static func - (lhs: Scalar, rhs: Scalar) -> Scalar {
+        Scalar(value: lhs.value - rhs.value)
+    }
+
+    mutating func move(by offset: Scalar) {
+        value += offset.value
+    }
+}
+
+@differentiable(reverse)
+private func unwrap(_ scalar: Scalar) -> Double {
+    scalar.value
+}
+
+final class DifferentiationTests: XCTestCase {
+    func testComputesValueWithGradient() {
+        let result = valueWithGradient(at: 4.0, of: quadratic)
+
+        XCTAssertEqual(result.value, 30.0, accuracy: 1e-12)
+        XCTAssertEqual(result.gradient, 11.0, accuracy: 1e-12)
+    }
+
+    func testComputesMultiArgumentGradient() {
+        let result = valueWithGradient(at: 3.0, 5.0, of: weightedPolynomial)
+
+        XCTAssertEqual(result.value, 29.0, accuracy: 1e-12)
+        XCTAssertEqual(result.gradient.0, 11.0, accuracy: 1e-12)
+        XCTAssertEqual(result.gradient.1, 4.0, accuracy: 1e-12)
+    }
+
+    func testCustomDifferentiableTypeCanBeUsedAcrossModuleBoundary() {
+        let gradient = gradient(at: Scalar(value: 7), of: unwrap)
+
+        XCTAssertEqual(gradient.value, 1.0, accuracy: 1e-12)
+    }
+}