public async Task GetFileBase64_ReturnsString() { // Arrange _regionService.Setup(x => x.DownloadFileAsync(It.IsAny <string>())).ReturnsAsync("file"); // Act var result = await _regionController.GetFileBase64("file"); var actual = (result as ObjectResult).Value; // Assert Assert.IsInstanceOf <OkObjectResult>(result); Assert.IsInstanceOf <string>(actual); }