Unit Testing C# Async Methods

This time I have a C# async method that should be tested. As you remember, async method must return Task or Task<>.  You can declare an async void method, but this should be used only for event handlers because you have no control on method execution and, the most important, its failure. Beside that, async void method is hard to test.

I have a simple async method that returns Task<int> instead of int in synchronous method (look at my previous post Unit Testing C# Synchronous Methods).

We must be happy that modern unit test frameworks allow to write async unit test where an async method is called asynchronously.

1. Check successful result

The async method being tested is called via await operator. This makes the code being executed in true asynchronous mode.

2.1. Check failure with ThrowsAsync<>

Unit test is awaiting for result from Assert.ThrowsAsync, that is awaiting for result from the method being tested. If you delete the inner async/await, the method would be executed in synchronous mode. If you omit the first outer await, the unit test method might finish before the code in NumberAsync would fail. So you will get wrong results!

2.2. Check failure with Record.ExceptionAsync

Unit Testing C# Synchronous Methods

When you need to unit test a method, you should check happy path (for example, the method returns a resulting value) and sad path (the method throws exception). Here I describe a basic usage of unit testing with Visual Studio 2017 and xUnit version 2.2.

The code being tested:

1. Check successful result (happy path) – it’s very straightforward.

2. Check fail when the method throws an exception (sad path)

If you have faced with MSTest, you might remember [ExpectedException] attribute. In this case MSTest waits for a particular exception would be thrown in a whole unit test method, but not in a specific line of code. Modern unit test frameworks have more graceful capabilities to catch the exception.

2.1. Using Throws<>

But this approach combines Act and Assert phases of unit test in one line of code. Richard Banks suggested a better way in his article Stop Using Assert.Throws in Your BDD Unit Tests.

2.2. Using Record.Exception

At first, I check that the exception was really caught, then check the type of that exception.

Next time I’ll tell about unit testing the asynchronous methods.

ASP.NET Identity. Part 2 – Customizing Entities

ASP.NET Identity gives a class ApplicationUser for storing data about users. It has a lot of properties defined in base class IdentityUser, such as Id, UserName, Email, PhoneNumber, etc. But when you need to add some extra properties, it becomes more complicated.

Entity Framework creates a database only once at first use. It does not recreate, nor modify it. We should use EF migrations to add new fields. Also it gives the possibility to change table names.

1. Add new properties in file Models\IdentityModels.cs

2. Open Package Manager Console and run command

EF will create folder Migrations and a couple of files: Configuration.cs and <timestamp>_InitialCreate.cs with code to create a default database structure.
3. Create new migration and give it a name

Visual Studio will open a file with two method to add and drop columns defined in step 1.
4. Apply EF migration to database.

Now I have the following database structure:

5. I want to enter first and last names during the registration process. So I’ll add two properties to class RegisterViewModel in file Models\AccountViewModels.cs

6. Add code to Views\Account\Register.cshtml file to display these them.

7. Change Register method in Account controller (file Controllers\AccountController.cs) to store them.

8. Also I want to display user’s first name on the top bar of the web application instead of his/her email. To do this we need to modify file Views\Shared\_LoginPartial.cshtml to get ApplicationUser via current user’s Id with the help of Owin context, then to show property FirstName. The final code looks like this:

ASP.NET Identity. Part 1 – Changing Default Database

When you create MVC project in Visual Studio 2017, you can use individual user accounts authentication that is shipped with MVC template. This implementation uses Entity Framework. By default, EF creates a database in SQL Server LocalDB with a name like aspnet-WebApp-<timestamp>.

To change the connection to database:
1. Open Web.config file
2. Find section <connectionStrings>
3. Modify the attribute connectionString in element with name DefaultConnection. Element will look like the following:

<add name="DefaultConnection" connectionString="Data Source=(local);Integrated Security=SSPI;Initial Catalog=AspNetIdentityDB;" providerName="System.Data.SqlClient"/>

If you dislike the name DefaultConnection, you should change it in Web.config file and in the constructor of ApplicationDbContext class (file Models\IdentityModels.cs).

Creating GitHub Project In Visual Studio 2017

My goal is to create a new solution and place it in GitHub. This can be done in few steps:

1. Create a GitHub account.
2. Install a GitHub extension for Visual Studio. I’ve downloaded it from https://visualstudio.github.com/
3. Start Visual Studio, open Team Explorer and connect to GitHub.

4. Create a new GitHub repository.

Click link, and enter data in the next form.

5. Switch back to Team Explorer. Click Create a new project or solution link.

6. Choose project type, give it a name. Step forward on wizard steps.

After that you will have the following structure in Visual Studio

and in a disk folder

Now you can write code, commit changes and push them to GitHub.

Converting List To IDataReader

I wrote about using SqlBulkCopy to fast load data from .NET into SQL Server database. This class needs a DataTable or IDataReader instance as a source. You can convert a C# List to DataTable (look here Converting List To DataTable). Now I’ll show a couple of examples how to convert List to IDataReader.

1. Straight implementation of IDataReader interface
I’ve seen a couple of good examples from Bruce Dunwiddie https://www.csvreader.com/posts/GenericListDataReader.cs and Venu Gopal http://technico.qnownow.com/custom-data-reader-to-bulk-copy-data-from-object-collection-to-sql-server/. Based on these two solutions I’ve made my one.

Now you can iterate through IDataReader like you do with SqlDataReader.

2. FastMember NuGet package

Thank you, Marc! it’s a good job https://github.com/mgravell/fast-member

You need to install NuGet package FastMember, add using FastMember; statement, and run this code.