Mocking Mcp Client Functions for Testing

[ethan-christensen-cag]

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Discussion Topic

I am just making the post to see if there are any suggestions on mocking for Mcp Clients with the .NET SDK. I am using MOQ for my testing and am having trouble simply mocking the ListToolsAsync() method on the client, with the main issue being that I cannot create instances on McpClientTool to use as a return type for the MOQ setup on the ListToolsAsync function call.

I am not the most versed in testing so I could very well be missing something. What I ended up doing to get it working was the following, targeting all the way down the the IMcpEndpoint class.

I should note I am not trying to spin up a test mcp server, but rather mock the returns from this McpClient Class. I could very well be missing something or making it more complicated than it needs to be.

var toolResults = new ListToolsResult {
    Tools = new List<Tool> {
        new() {
            Name = "MockTool",
            Title = "Mock Tool",
            Description = "This is a Mock Tool."
        }
    }
};

var mockClient = Mock<IMcpClient>();
mockClient
    .As<IMcpEndpoint>()
    .Setup(e => e.SendRequest(It.IsAny<JsonRpcRequest>(), It.IsAny<CancellationToken>()))
    .ReturnsAsync(new JsonRpcResponse { Result = JsonSerializer.SerializeToNode(toolResults)});