如何在单元测试中Mock GraphServiceClient并返回模拟响应？

问题场景 #

业务代码依赖GraphServiceClient获取域名注册商信息：

private GraphServiceClient gsc;

public RiskIQService(GraphServiceClient gsc)
{
    // 注意：原代码存在bug，未给私有字段赋值，需改为 this.gsc = gsc;
    gsc = gsc;
}

public async Task<string> getRegistrar(string domain)
{
    Microsoft.Graph.Models.Security.Hostname? response = (Microsoft.Graph.Models.Security.Hostname?) await gsc.Security.ThreatIntelligence.Hosts[domain].GetAsync();

    return response.Registrar;
}

尝试直接Mock GraphServiceClient时触发错误：

System.NotSupportedException: Unsupported expression: ... => ....GetAsync(null, CancellationToken.None) Non-overridable members (here: HostItemRequestBuilder.GetAsync) may not be used in setup / verification expressions.

原Mock代码：

private readonly Mock<GraphServiceClient> gscMock = new Mock<GraphServiceClient>();
var response = new Hostname(Registrar = "Registrar");
gscMock.Setup(x => x.Security.ThreatIntelligence.Hosts[It.IsAny<string>()].GetAsync(null, CancellationToken.None)).ReturnsAsync(response);

错误原因 #

Microsoft Graph SDK中的HostItemRequestBuilder.GetAsync是非虚方法，Moq仅支持Mock虚方法或接口定义的方法，直接对GraphServiceClient类进行链式Setup会触发非虚方法不支持的错误。

正确Mock方案 #

利用Graph SDK提供的各层级请求构建器接口，逐层Mock每个依赖节点：

// 1. Mock最底层的Host请求构建器，模拟GetAsync返回结果
var hostItemMock = new Mock<IHostItemRequestBuilder>();
var mockHostname = new Microsoft.Graph.Models.Security.Hostname { Registrar = "TestRegistrar" };
hostItemMock.Setup(x => x.GetAsync(It.IsAny<RequestConfiguration<DefaultQuerySettings>>(), It.IsAny<CancellationToken>()))
            .ReturnsAsync(mockHostname);

// 2. Mock Hosts集合构建器，索引器返回上面的Host请求构建器
var hostsCollectionMock = new Mock<IHostsCollectionRequestBuilder>();
hostsCollectionMock.Setup(x => x[It.IsAny<string>()])
                   .Returns(hostItemMock.Object);

// 3. Mock ThreatIntelligence构建器，返回Hosts集合构建器
var threatIntelligenceMock = new Mock<IThreatIntelligenceRequestBuilder>();
threatIntelligenceMock.Setup(x => x.Hosts)
                      .Returns(hostsCollectionMock.Object);

// 4. Mock Security构建器，返回ThreatIntelligence构建器
var securityMock = new Mock<ISecurityRequestBuilder>();
securityMock.Setup(x => x.ThreatIntelligence)
            .Returns(threatIntelligenceMock.Object);

// 5. 最后Mock GraphServiceClient，返回Security构建器
var gscMock = new Mock<GraphServiceClient>();
gscMock.Setup(x => x.Security)
       .Returns(securityMock.Object);

// 注入Mock对象到业务服务
var riskIQService = new RiskIQService(gscMock.Object);
// 执行测试
var result = await riskIQService.getRegistrar("test-domain.com");
// 断言结果
Assert.Equal("TestRegistrar", result);

额外注意 #

• 原业务代码的构造函数存在赋值错误，必须将gsc = gsc;改为this.gsc = gsc;，否则私有字段gsc始终为null，无法正常执行。
• 若使用的Graph SDK版本不同，接口名称可能略有差异，请以实际SDK定义为准。

内容的提问来源于stack exchange，提问作者Punter Vicky