How to test for exception in Nest?

Question

I am trying to test for the results of certain exceptions when Nest has a value in IGetResponse.OriginalException property.

I first set up the response:

var response = A.Fake<Nest.IGetResponse<Dictionary<string, object>>>();
A.CallTo(() => response.OriginalException).Returns(new Exception("Status code 404"));

Then the fake elastic client:

var client = A.Fake<Nest.IElasticClient>();
A.CallTo(client)
    .WithReturnType<Nest.IGetResponse<Dictionary<string, object>>>()
    .Returns(response);

The client gets injected into the class I am testing.

However, when stepping through the code, when the client is called it returns a faked response, but the OriginalException getter has no value. Its not null, but none of the properties has any value. I was expecting the OriginalException.Message to equal Status code 404.

I also tried setting the response object to:

var response = A.Fake<Nest.IGetResponse<Dictionary<string, object>>>();
A.CallTo(() => response.OriginalException.Message).Returns("Status code 404");

... with equally poor results.

How can I set the IGetResponse so I can evaluate OriginalException.Message in the class being tested?

More code was requested. I can show the entire test, and I will show the method being tested. Here is my entire test:

    [TestMethod]
    [ExpectedException(typeof(NotFoundException))]
    public void Get_ClientReturns404_ThrowsNotFoundException()
    {
        // setup
        var request = new DataGetRequest
        {
            CollectionName = string.Empty,
            DocumentType = string.Empty,
            DataAccessType = string.Empty
        };

        var response = A.Fake<Nest.IGetResponse<Dictionary<string, object>>>();
        A.CallTo(() => response.OriginalException.Message).Returns("Status code 404");

        var client = A.Fake<Nest.IElasticClient>();
        A.CallTo(client)
            .WithReturnType<Nest.IGetResponse<Dictionary<string, object>>>()
            .Returns(response);

        var elasticSearch = new ElasticSearch(null, client);

        // test
        var result = elasticSearch.Get(request);

        // assert
        Assert.Fail("Should have hit an exception.");
    }
}

And here is the method being tested:

    public async Task<Dictionary<string, object>> Get(DataGetRequest getRequest)
    {
        GetRequest request = new GetRequest(getRequest.CollectionName, getRequest.DocumentType, getRequest.Id);
        var response = await Client.GetAsync<Dictionary<string, object>>(request);

        if (response.OriginalException != null)
        {
            var message = response.OriginalException.Message;
            if (message.Contains("Status code 404"))
                throw new NotFoundException(String.Format("Not Found for id {0}", getRequest.Id));
            else
                throw new Exception(message);
        }                

        return response.Source;
    }

The error handling in the IF block is not very robust. Once the unit test works then the code will likely receive more love.

Nothing's popping out at me. Are you able to paste more code? Ideally a runnable test, but at least how you inject the client into the class you're testing, how you call that class, and what the called method does? — Blair Conrad, Nov 09 '18 at 20:25
@BlairConrad Done. Not sure how much help it will be, but you never know. — Sailing Judo, Nov 09 '18 at 20:33

Nkosi · Accepted Answer · 2018-11-10T01:08:15.980

The return type of the mocked client is wrong as the IElasticClient.GetAsync<> returns a Task<IGetResponse<T>>.

Task<IGetResponse<T>> GetAsync<T>(IGetRequest request, CancellationToken cancellationToken = default(CancellationToken)) where T : class;

Source

So the setup needs to return a Task derived result to allow the async code

var response = await Client.GetAsync<Dictionary<string, object>>(request);

to flow as expected.

For example

[TestMethod]
[ExpectedException(typeof(NotFoundException))]
public async Task Get_ClientReturns404_ThrowsNotFoundException() {

    //Arrange
    var originalException = new Exception("Status code 404");

    var response = A.Fake<Nest.IGetResponse<Dictionary<string, object>>>();
    A.CallTo(() => response.OriginalException).Returns(originalException);

    var client = A.Fake<Nest.IElasticClient>();
    A.CallTo(() => 
        client.GetAsync<Dictionary<string, object>>(A<IGetRequest>._, A<CancellationToken>._)
    ).Returns(Task.FromResult(response));

    var request = new DataGetRequest {
        CollectionName = string.Empty,
        DocumentType = string.Empty,
        DataAccessType = string.Empty
    };

    var elasticSearch = new ElasticSearch(null, client);

    // Act
    var result = await elasticSearch.Get(request);

    // Assert
    Assert.Fail("Should have hit an exception.");
}

Nice. And a bonus +1 for faking `GetAsync` directly rather than using the powerful, but potentially error-prone, `WithReturnType` syntax. — Blair Conrad, Nov 10 '18 at 17:31

How to test for exception in Nest?

1 Answers1