public void FileUploadIncorrectTest() { //Arrange var fileMock = new Mock <IFormFile>(); var content = "Content"; var fileName = "test.pdf"; var contentType = "Pdf"; var ms = new MemoryStream(); var writer = new StreamWriter(ms); writer.Write(content); writer.Flush(); ms.Position = 0; fileMock.Setup(_ => _.OpenReadStream()).Returns(ms); fileMock.Setup(_ => _.FileName).Returns(fileName); fileMock.Setup(_ => _.ContentType).Returns(contentType); fileMock.Setup(_ => _.Length).Returns(ms.Length); var iFormFileFake = fileMock.Object; FileUpload upload = new FileUpload("C:\\Users\\Ondrej\\source\\repos\\OndrejMicina\\eshop\\eshop\\wwwroot", "Tests", "image"); //Act var result = upload.CheckFileContent(iFormFileFake); //ocakava false Assert.False(result); }