How to verify that a class is serializable?

Recently I've came into investigating a failing End-to-End test that was failing inside the WCF service with an exception. The exception was related to WCF serialization of the return type of the service. As usually I decided to tackle this issue in the TDD way:

1. Write a fialing test that reproduces the issue
2. Write the minimum amount of code to make the test pass
3. Refactor if needed

I already had a failing End to End test that was failing, but it was a heavy and complex test. All I wanted to a small, fast, isolated and reproducible test that would test only the serialization of that class. We're using FluentAssertions library for readable and intuitive assertions in our unit tests I checked whether it contains a way to verify whether a class would be successfully serialized in WCF. Unfortunately, it had two similar methods:

I need to explain what these methods exactly do for those who are not familiar with them:

1. Serialize the instance using the selected serialization method: binary or XML
2. Deserialize the result of the above serialization
3. Compare the values of the resulted instance with the original one

It was exactly what I needed, but these methods use different serialization methods than WCF. WCF uses DataContract serialization. I decided to contribute to FluentAssertions library and to add the required method. Dennis Doomen generously accepted my pull request and the new method is available in the official nuget package starting from version 4.5.0. Here how it looks like with the new method:


Last but not least: if you encounter into WCF serialization issues, take a look at my post from 2010 with some WCF Serialization Tips.

How to mock file system in tests?

You are probably familiar with System.IO namespace in .NET Framework. It contains useful API for file system operations. Unfortunately, most of its methods are static and thus it is impossible to mock them. In this post I would like to show how we write testable code that works with file system.

Let's see the below simple class that copies a file to a destination directory. If the destination directory does not exist, it creates the directory and then copies the file to the destination.

In order to make our code testable we'll use System.IO.Abstractions library which can be installed from nuget:

package-install System.IO.Abstractions

It provides IFileSystem interface with all the useful interfaces on it:
It will allow us to refactor our class by injecting the IFileSystem into our constructor: As you can see from the above code, all the classes and methods on the System.IO.Abstractions are similar to those on the System.IO. So the transition is very smooth. You also noticed that the IFileSystem is injected via internal constructor, which we'll use in unit tests shortly. Public constructor will be used in our real code and it injects actual implementation of IFileSystem which is FileSystem class. The last part is the unit test. There is complementary library that contains in memory implementation of IFileSystem interface. It can be installed from nuget as well:
Install-Package System.IO.Abstractions.TestingHelpers

In addition to the implementation of IFileSystem interface, it contains convenient methods for adding files and directories (in memory, of course). So let's see how our unit test looks like: We can even assert, that the file was copied and it exists in the destination folder. The library also works well with all existing stream Read/Write operations.
Credits for the library go to: Tatham Oddie

Enjoy coding, Boris Modylevsky