我正在尝试为以下 AspNetCore 控制器方法编写单元测试：[HttpGet]public async Task<IActionResult> GetFile(string id){    FileContent file = await fileRepository.GetFile(id);    if (file == null)        return NotFound();    Response.Headers.Add("Content-Disposition", file.FileName);    return File(file.File, file.ContentType);}文件内容类：public class FileContent{    public FileContent(string fileName, string contentType, byte[] file)    {        FileName = fileName;        ContentType = contentType;        File = file;    }    public string FileName { get; }    public string ContentType { get; }    public byte[] File { get; }}这是测试初始化：[TestInitialize]public void TestInitialize(){    repositoryMock = new Mock<IFileRepository>();    controller = new FilesController(repositoryMock.Object);    var httpContext = new Mock<HttpContext>(MockBehavior.Strict);    var response = new Mock<HttpResponse>(MockBehavior.Strict);    var headers = new HeaderDictionary();    response.Setup(x => x.Headers).Returns(headers);    httpContext.SetupGet(x => x.Response).Returns(response.Object);    controller.ControllerContext = new ControllerContext(new ActionContext(httpContext.Object, new RouteData(), new ControllerActionDescriptor()));}及测试方法：[TestMethod]public async Task GetShouldReturnCorrectResponse(){    repositoryMock        .Setup(x => x.GetFile(It.IsAny<string>(), null))        .ReturnsAsync(new FileContent("test.txt", "File Content.", Encoding.UTF8.GetBytes("File Content.")));    IActionResult response = await controller.GetFile(DocumentId);    // .. some assertions}在以下控制器线路上测试失败：return File(file.File, file.ContentType);例外情况：System.FormatException：标头在索引 0 处包含无效值：“文件内容”。在 Microsoft.Net.Http.Headers.HttpHeaderParser`1.ParseValue(StringSegment value, Int32& index) 在 Microsoft.AspNetCore.Mvc.FileContentResult..ctor(Byte[] fileContents, String contentType) 在 Microsoft.AspNetCore.Mvc.ControllerBase。文件（字节[]文件内容，字符串内容类型，字符串文件下载名称）我不明白这里出了什么问题。请指教。