[camera_avfoundation] Add test for @sendable completion handler

- Updates MockCaptureDevice to use @sendable on setExposureTargetBias,
  keeping it in sync with the CaptureDevice protocol requirement.
- Adds testSetExposureTargetBias_completionHandlerIsInvoked to exercise
  the non-nil handler path and serve as a compile-time regression guard:
  if @sendable is removed from the protocol the mock conformance breaks.

Author: teclas-gif

packages/camera/camera_avfoundation/example/ios/RunnerTests/CameraExposureTests.swift

@@ -124,6 +124,26 @@ final class CameraExposureTests: XCTestCase {
     XCTAssertTrue(setExposureTargetBiasCalled)
   }
 
+  func testSetExposureTargetBias_completionHandlerIsInvoked() {
+    // Regression test: the completion handler must be @Sendable to match
+    // AVCaptureDevice's signature (Swift 6 requirement).
+    // MockCaptureDevice conforms to CaptureDevice, so a compilation failure
+    // here means the protocol and mock have diverged.
+    let (_, mockDevice, _) = createCamera()
+
+    let expectation = expectation(description: "completion handler invoked")
+
+    mockDevice.setExposureTargetBiasStub = { _, handler in
+      handler?(CMTime(value: 1, timescale: 1))
+    }
+
+    mockDevice.setExposureTargetBias(1.0) { _ in
+      expectation.fulfill()
+    }
+
+    waitForExpectations(timeout: 1.0)
+  }
+
   func testMaximumExposureOffset_returnsDeviceMaxExposureTargetBias() {
     let (camera, mockDevice, _) = createCamera()
 

packages/camera/camera_avfoundation/example/ios/RunnerTests/Mocks/MockCaptureDevice.swift

@@ -18,7 +18,7 @@ class MockCaptureDevice: NSObject, CaptureDevice {
   var setFocusPointOfInterestStub: ((CGPoint) -> Void)?
   var setExposureModeStub: ((AVCaptureDevice.ExposureMode) -> Void)?
   var setExposurePointOfInterestStub: ((CGPoint) -> Void)?
-  var setExposureTargetBiasStub: ((Float, ((CMTime) -> Void)?) -> Void)?
+  var setExposureTargetBiasStub: ((Float, (@Sendable (CMTime) -> Void)?) -> Void)?
   var isExposureModeSupportedStub: ((AVCaptureDevice.ExposureMode) -> Bool)?
   var setVideoZoomFactorStub: ((CGFloat) -> Void)?
   var lockForConfigurationStub: (() throws -> Void)?
@@ -99,7 +99,7 @@ class MockCaptureDevice: NSObject, CaptureDevice {
     set { setExposurePointOfInterestStub?(newValue) }
   }
 
-  func setExposureTargetBias(_ bias: Float, completionHandler handler: ((CMTime) -> Void)? = nil) {
+  func setExposureTargetBias(_ bias: Float, completionHandler handler: (@Sendable (CMTime) -> Void)? = nil) {
     setExposureTargetBiasStub?(bias, handler)
   }