测试调用返回“值不能为空”的异步方法

Question

我有一个异步方法，我正在尝试对其进行单元测试，特别是我想测试异步方法是否返回NoContent 响应，因为没有找到客户实体。这是有问题的方法：

    [HttpGet]
    [Route("customers/{customerNumber}")]
    public virtual async Task<IHttpActionResult> Get([FromUri] CustomerNumber customerNumber)
    {
        var customerEntitiesList = _tableStorageService.GetCustomerEntities(customerNumber);
        var customersList = customerEntitiesList.Select(customerEntity => customerEntity.PartitionKey).ToList();
        if (customersList.Any()) {
            return await Task.FromResult(Ok(customersList));
        }
        return await Task.FromResult(ResponseMessage(Request.CreateErrorResponse(HttpStatusCode.NoContent, "No content found.")));
    }

澄清一下，CustomerNumber 是一个字符串表示类，如下所示：

[DebuggerDisplay("{ToString()}")]
public class CustomerNumber
{
    public CustomerNumber(string customerNumber);

    public static bool TryParse(string customerNumber, out CustomerNumber parsedCustomerNumber);
    public override string ToString();

    public static implicit operator string(CustomerNumber customerNumber);
    public static implicit operator CustomerNumber(string customerNumber);
}

这是单元测试：

    [Test]
    public async Task Should_Return_No_Content_If_Customer_Entities_Are_Not_Found()
    {
        const string customerNumber = "WP0000000000";
        var customerEntitiesStub = new List<CustomerEntity>();
        A.CallTo(() => _tableStorageServiceDummy.GetCustomerEntities(customerNumber)).Returns(customerEntitiesStub);

        var result = await _companyController.Get(customerNumber);

        ((ResponseMessageResult)result).Response.StatusCode.Should().Be(HttpStatusCode.NoContent);
    }

当我运行这个测试时，它甚至在完成之前就失败了，并出现错误System.ArgumentNullException : Value cannot be null.。为什么会发生这种情况，我该如何解决它以便我可以断言结果？谢谢！

Answer 1

模拟设置为期望 string，但实际方法具有 CustomerNumber 参数。在那里开始调查。

由于设置不匹配，当调用 GetCustomerEntities 时，customerEntitiesList 将是 null。

假设CustomerNumber 可以从字符串隐式转换，那么测试应该配置一个实际的CustomerNumber 实例。

[Test]
public async Task Should_Return_No_Content_If_Customer_Entities_Are_Not_Found() {
    const CustomerNumber customerNumber = "WP0000000000";
    var customerEntitiesStub = new List<CustomerEntity>();
    A.CallTo(() => _tableStorageServiceDummy.GetCustomerEntities(customerNumber)).Returns(customerEntitiesStub);

    var result = await _companyController.Get(customerNumber);

    ((ResponseMessageResult)result).Response.StatusCode.Should().Be(HttpStatusCode.NoContent);
}

在单独的不是该动作的设计中，将结果包装在任务中。目前没有理由使该操作异步。

[HttpGet]
[Route("customers/{customerNumber}")]
public virtual IHttpActionResult Get([FromUri] CustomerNumber customerNumber)
{
    var customerEntitiesList = _tableStorageService.GetCustomerEntities(customerNumber);
    var customersList = customerEntitiesList.Select(customerEntity => customerEntity.PartitionKey).ToList();
    if (customersList.Any()) {
        return Ok(customersList);
    }
    return Request.CreateErrorResponse(HttpStatusCode.NoContent, "No content found.");
}

并相应地更新测试。