July 2017 – Andrey Zavadskiy – SQL and .NET developer, trainer, speaker

July 16, 2017July 17, 2017

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).

public async Task<int> GetNumberAsync(int number)
{
    await Task.Delay(100);

    if (number < 0)
    {
        throw new ArgumentException();
    }

    return number;
}

public async Task<int> GetNumberAsync(int number)

{

await Task.Delay(100);

if (number < 0)

{

throw new ArgumentException();

}

return number;

}

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

[Fact]
public async Task GetNumberAsync_Success()
{
    // arrange
    var sut = new SystemUnderTest();
    // act
    int actual = await sut.GetNumberAsync(5);
    // assert
    Assert.Equal(5, actual);
}

[Fact]

public async Task GetNumberAsync_Success()

{

// arrange

var sut = new SystemUnderTest();

// act

int actual = await sut.GetNumberAsync(5);

// assert

Assert.Equal(5, actual);

}

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<>

[Fact]
public async Task GetNumberAsync_Fail_Throws()
{
    // arrange
    var sut = new SystemUnderTest();
    // act & assert
    await Assert.ThrowsAsync<ArgumentException>(async () => await sut.GetNumberAsync(-1));
}

[Fact]

public async Task GetNumberAsync_Fail_Throws()

{

// arrange

var sut = new SystemUnderTest();

// act & assert

await Assert.ThrowsAsync<ArgumentException>(async () => await sut.GetNumberAsync(-1));

}

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

[Fact]
public async Task GetNumberAsync_Fail_Record()
{
    // arrange
    var sut = new SystemUnderTest();
    // act
    var exception = await Record.ExceptionAsync(async () => await sut.GetNumberAsync(-1));
    // assert
    Assert.NotNull(exception);
    Assert.IsType<ArgumentException>(exception);
}

[Fact]

public async Task GetNumberAsync_Fail_Record()

{

// arrange

var sut = new SystemUnderTest();

// act

var exception = await Record.ExceptionAsync(async () => await sut.GetNumberAsync(-1));

// assert

Assert.NotNull(exception);

Assert.IsType<ArgumentException>(exception);

}

July 15, 2017May 5, 2018

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:

public int GetNumber(int number)
{
    if (number < 0)
    {
        throw new ArgumentException();
    }

    return number;
}

public int GetNumber(int number)

{

if (number < 0)

{

throw new ArgumentException();

}

return number;

}

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

[Fact]
public void GetNumber_Success()
{
    // arrange
    var sut = new SystemUnderTest();
    // act
    int actual = sut.GetNumber(5);
    // assert
    Assert.Equal(5, actual);
}

[Fact]

public void GetNumber_Success()

{

// arrange

var sut = new SystemUnderTest();

// act

int actual = sut.GetNumber(5);

// assert

Assert.Equal(5, actual);

}

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<>

[Fact]
public void GetNumber_Fail_Throws()
{
    // arrange
    var sut = new SystemUnderTest();
    // act & assert
    Assert.Throws<ArgumentException>(() => sut.GetNumber(-1));
}

[Fact]

public void GetNumber_Fail_Throws()

{

// arrange

var sut = new SystemUnderTest();

// act & assert

Assert.Throws<ArgumentException>(() => sut.GetNumber(-1));

}

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

[Fact]
public void GetNumber_Fail_Record()
{
    // arrange
    var sut = new SystemUnderTest();
    // act
    var exception = Record.Exception(() => sut.GetNumber(-1));
    // assert
    Assert.NotNull(exception);
    Assert.IsType<ArgumentException>(exception);
}

[Fact]

public void GetNumber_Fail_Record()

{

// arrange

var sut = new SystemUnderTest();

// act

var exception = Record.Exception(() => sut.GetNumber(-1));

// assert

Assert.NotNull(exception);

Assert.IsType<ArgumentException>(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.

July 11, 2017July 13, 2017

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.

July 3, 2017November 5, 2020

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.

public class ListDataReader<T> : IDataReader
        where T : class
{
    #region Private fields
    private IEnumerator<T> _iterator;
    private List<PropertyInfo> _properties = new List<PropertyInfo>();
    #endregion

    #region Public properties
    #endregion

    #region Constructors
    public ListDataReader(IEnumerable<T> list)
    {
        this._iterator = list.GetEnumerator();

        _properties.AddRange(
            typeof(T).GetProperties(
                BindingFlags.GetProperty |
                BindingFlags.Instance |
                BindingFlags.Public |
                BindingFlags.DeclaredOnly
                )
            );
    }
    #endregion

    #region IDataReader implementation
    public int Depth { get; }
    public bool IsClosed { get; }
    public int RecordsAffected { get; }

    public void Close()
    {
        _iterator.Dispose();
    }

    public DataTable GetSchemaTable()
    {
        throw new NotImplementedException();
    }

    public bool NextResult()
    {
        throw new NotImplementedException();
    }

    public bool Read()
    {
        return _iterator.MoveNext();
    }
    #endregion

    #region IDisposable implementation
    public void Dispose()
    {
        Close();
    }
    #endregion

    #region IDataRecord
    public string GetName(int i)
    {
        return _properties[i].Name;
    }

    public string GetDataTypeName(int i)
    {
        throw new NotImplementedException();
    }

    public Type GetFieldType(int i)
    {
        return _properties[i].PropertyType;
    }

    public object GetValue(int i)
    {
        return _properties[i].GetValue(_iterator.Current, null);
    }

    public int GetValues(object[] values)
    {
        int numberOfCopiedValues = Math.Max(_properties.Count, values.Length);

        for (int i = 0; i < numberOfCopiedValues; i++)
        {
            values[i] = GetValue(i);
        }

        return numberOfCopiedValues;
    }

    public int GetOrdinal(string name)
    {
        var index = _properties.FindIndex(p => p.Name == name);

        return index;
    }

    public bool GetBoolean(int i)
    {
        return (bool) GetValue(i);
    }

    public byte GetByte(int i)
    {
        return (byte) GetValue(i);
    }

    public long GetBytes(int i, long fieldOffset, byte[] buffer, int bufferoffset, int length)
    {
        throw new NotImplementedException();
    }

    public char GetChar(int i)
    {
        return (char) GetValue(i);
    }

    public long GetChars(int i, long fieldoffset, char[] buffer, int bufferoffset, int length)
    {
        throw new NotImplementedException();
    }

    public Guid GetGuid(int i)
    {
        return (Guid) GetValue(i);
    }

    public short GetInt16(int i)
    {
        return (short) GetValue(i);
    }

    public int GetInt32(int i)
    {
        return (int) GetValue(i);
    }

    public long GetInt64(int i)
    {
        return (long) GetValue(i);
    }

    public float GetFloat(int i)
    {
        return (float) GetValue(i);
    }

    public double GetDouble(int i)
    {
        return (double) GetValue(i);
    }

    public string GetString(int i)
    {
        return (string) GetValue(i);
    }

    public decimal GetDecimal(int i)
    {
        return (decimal) GetValue(i);
    }

    public DateTime GetDateTime(int i)
    {
        return (DateTime) GetValue(i);
    }

    public IDataReader GetData(int i)
    {
        throw new NotImplementedException();
    }

    public bool IsDBNull(int i)
    {
        return GetValue(i) == null;
    }

    public int FieldCount
    {
        get { return _properties.Count; } 
    }

    object IDataRecord.this[int i]
    {
        get { return GetValue(i); }
    }

    object IDataRecord.this[string name]
    {
        get { return GetValue(GetOrdinal(name)); }
    }
    #endregion
}

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public class ListDataReader<T> : IDataReader

where T : class

{

#region Private fields

private IEnumerator<T> _iterator;

private List<PropertyInfo> _properties = new List<PropertyInfo>();

#endregion

#region Public properties

#endregion

#region Constructors

public ListDataReader(IEnumerable<T> list)

{

this._iterator = list.GetEnumerator();

_properties.AddRange(

typeof(T).GetProperties(

BindingFlags.GetProperty |

BindingFlags.Instance |

BindingFlags.Public |

BindingFlags.DeclaredOnly

)

);

}

#endregion

#region IDataReader implementation

public int Depth { get; }

public bool IsClosed { get; }

public int RecordsAffected { get; }

public void Close()

{

_iterator.Dispose();

}

public DataTable GetSchemaTable()

{

throw new NotImplementedException();

}

public bool NextResult()

{

throw new NotImplementedException();

}

public bool Read()

{

return _iterator.MoveNext();

}

#endregion

#region IDisposable implementation

public void Dispose()

{

Close();

}

#endregion

#region IDataRecord

public string GetName(int i)

{

return _properties[i].Name;

}

public string GetDataTypeName(int i)

{

throw new NotImplementedException();

}

public Type GetFieldType(int i)

{

return _properties[i].PropertyType;

}

public object GetValue(int i)

{

return _properties[i].GetValue(_iterator.Current, null);

}

public int GetValues(object[] values)

{

int numberOfCopiedValues = Math.Max(_properties.Count, values.Length);

for (int i = 0; i < numberOfCopiedValues; i++)

{

values[i] = GetValue(i);

}

return numberOfCopiedValues;

}

public int GetOrdinal(string name)

{

var index = _properties.FindIndex(p => p.Name == name);

return index;

}

public bool GetBoolean(int i)

{

return (bool) GetValue(i);

}

public byte GetByte(int i)

{

return (byte) GetValue(i);

}

public long GetBytes(int i, long fieldOffset, byte[] buffer, int bufferoffset, int length)

{

throw new NotImplementedException();

}

public char GetChar(int i)

{

return (char) GetValue(i);

}

public long GetChars(int i, long fieldoffset, char[] buffer, int bufferoffset, int length)

{

throw new NotImplementedException();

}

public Guid GetGuid(int i)

{

return (Guid) GetValue(i);

}

public short GetInt16(int i)

{

return (short) GetValue(i);

}

public int GetInt32(int i)

{

return (int) GetValue(i);

}

public long GetInt64(int i)

{

return (long) GetValue(i);

}

public float GetFloat(int i)

{

return (float) GetValue(i);

}

public double GetDouble(int i)

{

return (double) GetValue(i);

}

public string GetString(int i)

{

return (string) GetValue(i);

}

public decimal GetDecimal(int i)

{

return (decimal) GetValue(i);

}

public DateTime GetDateTime(int i)

{

return (DateTime) GetValue(i);

}

public IDataReader GetData(int i)

{

throw new NotImplementedException();

}

public bool IsDBNull(int i)

{

return GetValue(i) == null;

}

public int FieldCount

{

get { return _properties.Count; }

}

object IDataRecord.this[int i]

{

get { return GetValue(i); }

}

object IDataRecord.this[string name]

{

get { return GetValue(GetOrdinal(name)); }

}

#endregion

}

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

using (IDataReader reader = new ListDataReader<Client>(clients))
{
    while (reader.Read())
    {
        ...
    }
}

using (IDataReader reader = new ListDataReader<Client>(clients))

{

while (reader.Read())

{

...

}

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.

using (var reader = ObjectReader.Create(clients))
{
    while (reader.Read())
    {
        ...
    }
}

using (var reader = ObjectReader.Create(clients))

{

while (reader.Read())

{

...

}