如何测试具有私有方法依赖项的公共函数？

Question

I'm trying to test a public method (Method A) that consumes an HttpClient to access an external API. This public method calls a private method (Method B) of the same class to get an Access Token that is required by the HttpClient of Method A to send the request. The problem I am having is that I am creating a mock of the HttpClientFactory interface in order to test the response of the Method A, but in order for Method B get the token it needs its own instance of HttpClient. Therefore, the mock instance created in the Test method will be used by the Method B as well, and it will fail trying to get the Access Token. The following code makes the scenario more clear.

Method to be tested (Method A):

 public async Task<HttpResponseMessage> SendAsync(string requestUri, string siteName, int accountId)
{
  try
  {
    var accessToken = await GetTokenAsync(siteName, accountId);
    if (accessToken == null)
      throw new ArgumentNullException("Error Sending request - Could not find an access token");

    var request = new HttpRequestMessage(HttpMethod.Get, $"{accessToken.Api}{requestUri}");

    request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", accessToken.Accesstoken);

    var httpClient = _httpClientFactory.CreateClient();
    return await httpClient.SendAsync(request);
  }
  catch (Exception e)
  {
    throw new Exception("Error Sending request.", e);
  }
}

Test Method:

[Fact]
public async Task ShouldReturnHttpResponseMessage_OnSendAsync()
{

  //_jaClientMock.Setup(x => x.GetTokenAsync(It.IsAny<string>(), It.IsAny<int>())).Verifiable();

  _appSettingsMock.Setup(x => x.Value)
    .Returns(GetValidFakeAppSettings());

  HttpResponseMessage expectedResponse = GetListOfContacts(HttpStatusCode.OK, false);
  _httpClientFactoryMock.Setup(x => x.CreateClient())
    .Returns(GetMockedHttpClient(expectedResponse));

  var response = await _jaClient.SendAsync("someurl", "siteName", 1000);

  response.IsSuccessStatusCode.ShouldBeTrue();
}

The private Method (Method B):

 private async Task<AccessToken> GetTokenAsync(string siteName, int accountId)
{
  try
  {
    if (_cache.TryGetValue(GetCacheKeyForToken(siteName, accountId), out AccessToken value))
      return value;
    ....

    var httpClient = _httpClientFactory.CreateClient();
    var response = await httpClient.SendAsync(request);

    if (response.IsSuccessStatusCode)
    {
      accessToken = await response.Content.ReadAsAsync<AccessToken>();
    }

    .....  
    return accessToken;
  }
  catch (Exception e)
  {
    throw new Exception("Error Getting an Access Token.", e);
  }
}

Any idea How I can test Method A?

Answer 1

There ain't no such thing as a free lunch - if one wants to unit-test some code with external dependencies, then each and every of those external dependencies has to be mocked .

Or one can go one step up the test pyramid to integration tests (though it is not our case, probably).

So, you could:

1. Either mock the Token response in the _httpClientFactory the same way you mock it for the SendAsync ( ..._httpClientFactoryMock.Setup(x => x.CreateClient()).Returns(GetMockedHttpClient(expectedResponse));... )

2. Or reorganize code in such a manner that tokens are not retrieved directly from API - create some single-method ITokenProvider interface that will be a bit easier to mock.

    public interface ITokenProvider { public async Task<AccessToken> GetTokenAsync(string siteName, int accountId); } ... public async Task<HttpResponseMessage> SendAsync(string requestUri, string siteName, int accountId) { try { var accessToken = await _tokenProvider.GetTokenAsync(siteName, accountId); ... [Fact] public async Task ShouldReturnHttpResponseMessage_OnSendAsync() { var tokenProviderMock = new Mock<ITokenProvider>() .Setup(o => o.GetTokenAsync("siteName", 1000)) .Returns(Constants.AllowedToken); _jaClient = new JaClient(tokenProviderMock.Object);...