tests.cs

public abstract class Testing : DbConnectionWrapper
{
    public bool CtorCalled { get; set; }

    protected Testing(IDbConnection innerConnection)
        : base(innerConnection)
    {
        CtorCalled = true;
    }
}

[Test]
public void Abstract_Class_Ctor_Called_With_Inner_Connection()
{
    var t = _conn.As<Testing>();
    Assert.True(t.CtorCalled); // fails
}

[Test]
public void Abstract_Class_Has_Inner_Connection()
{
    var t = _conn.As<Testing>();

    // throws null reference exception
    var connectionString = t.ConnectionString;

    Assert.NotNull(connectionString);
}