Evil Code #008: Property Instance

It has been long since I blogged on Evil Code series. Time to check one again now. Consider two samples of code.

Sample 1

public class AnotherClass
{
public MyClass ClassInstance{get;set;}
}

public class TestClass1
{
public AnotherClass AnotherClass{get;set;}
public int Id
{
get=> AnotherClass.ClassInstance.Id;
set=> AnotherClass.ClassInstance.Id=value;
}
}

public class MyClass
{
public int Id{get;set;}
}

Sample 2

public class AnotherClass
{
public MyStruct StructInstance{get;set;}
}

public class TestClass2
{
public AnotherClass AnotherClass{get;set;}
public int Id
{
get=> AnotherClass.StructInstance.Id;
set=> AnotherClass.StructInstance.Id=value;
}
}
public struct MyStruct
{
public int Id{get;set;}
}

How differently would two of the code samples given below behave ?

Well, Sample 1 compiles and Sample 2 doesn’t. Why ?? Sample 2, in fact raises following error.

Cannot modify the return value of 'AnotherClass.StructInstance' because it is not a variable

Could you reason why ?

If you look into the two Sample codes, there is a significant difference. MyStruct, used by Sample 2 is a value type. This means that when you are are in fact accessing a copy of StructInstance and not the valeu itself ( as you would have had it been a class – reference type).
Any change made in the property is made on the Copy instance, and then disregarded, leaving the original value unchanged.

This is the reason compiler warns you against.

Exploring Randomize.Net

Randomize.Net provides an easy and lightweight extensions for System.Random for creating random instances of any given Type T, with generated random value. This can be highly useful for generating POCO’s to test your sample code, including LINQ queries against. The API has been designed to make it extremely simple and devoid of any complex syntax.

Generating Random Instances

For Example,

// Primitive Types
var _random = new Random();_
var randomString = _random.GenerateInstance<string>();
var randomInt32 = _random.GenerateInstance<Int32>();

// Output
// randomString = OfuQ42CoIe
// randomInt32 = 239016499

Randomize.Net works with User Defined Types as well, including nested User Defined Types.

public class SampleClass
{
public string StringProperty{get;set;}
public int Int32Property {get;set;}
public char CharProperty {get;set;}
}

public class AnotherSampleClass
{
public SampleClass SampleClassProperty{get;set;}
public string StringProperty{get;set;}
}

var sampleClass = _random.GenerateInstance<SampleClass>();
var anotherSampleClass = _random.GenerateInstance<AnotherSampleClass>();

/* Output
* sampleClass.StringProperty = ORCPiyNoy5
* sampleClass.Int32Property = -1461704929
* sampleClass.CharProperty = q
*
* anotherSampleClass.StringProperty = D5wfOfQhAK
* anotherSampleClass.SampleClassProperty.StringProperty = DC7ArGwDj5
* anotherSampleClass.SampleClassProperty.Int32Property = -1311605510
* anotherSampleClass.SampleClassProperty.CharProperty = y
*/

Randomize.Net also supports generation of Collections.

// Method Signature
public static IEnumerable<T> GenerateCollection<T>(this Random source,int count = 1)

//Example
var sampleClassCollection = _random.GenerateCollection<SampleClass>(5);

// sampleClassCollection.Count = 5

Further examples on Randomize.Net would follow soon. If you are interested in looking at the code you can access it my Github.

Mock RestClient.ExecuteAsync

RestSharp is not a stranger to developers, so is the usage. What this posts aims to explore is how to do Unit Test a method, involving a RestClient.ExecuteAsync call. To be more precise, the post explores how to mock the RestClient for the method.

Let’s consider the following code, taken from VSPostman, one of the side projects I am working on.

public async Task Get(string url)
{
if (string.IsNullOrWhiteSpace(url) || _parameterDictionary.Values.Contains(null)) throw new ArgumentNullException();

_restClient.BaseUrl = new Uri(url); // _restClient is an instance of RestClient
_restRequest.Method = Method.GET;
var _returnValue = new ResponseObject();
if(_parameterDictionary?.Count==0)
_restRequest.Parameters.AddRange(_parameterDictionary?.Select(x => new Parameter() {Name = x.Key, Value = x.Value }));
var tcs = new TaskCompletionSource();
var watch = Stopwatch.StartNew();
_restClient.ExecuteAsync(_restRequest, response =>
{
_returnValue.ContendType = response.ContentType;
_returnValue.ResponseString = response.Content;
_returnValue.StatusCode = response.StatusCode;
_returnValue.StatusDescription = response.StatusDescription;
_returnValue.ResponseTime = watch.Elapsed;
_returnValue.Length = response.ContentLength;
if (response.Headers != null)
_returnValue.Headers = response.Headers.ToDictionary(x => x.Name, y => y.Value as string);

tcs.SetResult(_returnValue);
});
return await tcs.Task;
}

As observed, the code raises a GET Request using the ReshSharp library. If I was using TDD and writing a Unit Test case for this method, how would I approach it ? How would I mock the RestSharp library calls ?

Of course, it is easy to understand that we need to create the mock object of IRestClient. But how do we create a response ? For this we attach a call back.

var expected = "response content";
var expectedBytes = Encoding.UTF8.GetBytes(expected);
Mock restClient = new Mock();
restClient.Setup(x => x.ExecuteAsync(
It.IsAny(),
It.IsAny<Action<IRestResponse, RestRequestAsyncHandle>>()))
.Callback<IRestRequest, Action<IRestResponse, RestRequestAsyncHandle>>((request, callback) =>
{
callback(new RestResponse { Content= expected }, null);
});
// act
var clientService = new ClientServiceUsingRestSharp(restClient.Object);
var actualResponse = await clientService.Get($"http://www.google.com");

That would be all you need. The callback would ensure you get the response from the mock object.