Public ReadOnly Property Keys As ICollection(Of TKey)

public ICollection<TKey> Keys {get;}

List<KeyValuePair<int, string>> sample = new List<KeyValuePair<int, string>>();
for (int i = 0; i < 20; i++)
    sample.Add(new KeyValuePair<int,string>(i, i.ToString()));

using (BPlusTree<int, string> data = Create(Options))
{
    data.AddRange(sample);
    //Key collection
    Assert.AreEqual(data.Count, data.Keys.Count);
    Assert.IsTrue(data.Keys.IsReadOnly);
    for (int i = 0; i < sample.Count && i < 5; i++)
        Assert.IsTrue(data.Keys.Contains(sample[i].Key));

    IEnumerator<int> ek = data.Keys.GetEnumerator();
    Assert.IsTrue(ek.MoveNext());
    int firstkey = ek.Current;
    Assert.IsTrue(ek.MoveNext());
    Assert.AreNotEqual(firstkey, ek.Current);
    ek.Reset();
    Assert.IsTrue(ek.MoveNext());
    Assert.AreEqual(firstkey, ek.Current);
    Assert.AreEqual(firstkey, ((System.Collections.IEnumerator) ek).Current);

    //Value collection
    Assert.AreEqual(data.Count, data.Values.Count);
    Assert.IsTrue(data.Values.IsReadOnly);
    for (int i = 0; i < sample.Count && i < 5; i++)
        Assert.IsTrue(data.Values.Contains(sample[i].Value));

    IEnumerator<string> ev = data.Values.GetEnumerator();
    Assert.IsTrue(ev.MoveNext());
    string firstvalue = ev.Current;
    Assert.IsTrue(ev.MoveNext());
    Assert.AreNotEqual(firstvalue, ev.Current);
    ev.Reset();
    Assert.IsTrue(ev.MoveNext());
    Assert.AreEqual(firstvalue, ((System.Collections.IEnumerator) ev).Current);
}

Dim sample As New List(Of KeyValuePair(Of Integer, String))()
Dim i As Integer = 0
While i < 20
    sample.Add(New KeyValuePair(Of Integer, String)(i, i.ToString()))
    System.Math.Max(System.Threading.Interlocked.Increment(i),i - 1)
End While

Using data As BPlusTree(Of Integer, String) = Create(Options)
    data.AddRange(sample)
    'Key collection
    Assert.AreEqual(data.Count, data.Keys.Count)
    Assert.IsTrue(data.Keys.IsReadOnly)
    Dim i As Integer = 0
    While i < sample.Count AndAlso i < 5
        Assert.IsTrue(data.Keys.Contains(sample(i).Key))
        System.Math.Max(System.Threading.Interlocked.Increment(i),i - 1)
    End While

    Dim ek As IEnumerator(Of Integer) = data.Keys.GetEnumerator()
    Assert.IsTrue(ek.MoveNext())
    Dim firstkey As Integer = ek.Current
    Assert.IsTrue(ek.MoveNext())
    Assert.AreNotEqual(firstkey, ek.Current)
    ek.Reset()
    Assert.IsTrue(ek.MoveNext())
    Assert.AreEqual(firstkey, ek.Current)
    Assert.AreEqual(firstkey, (DirectCast(ek, System.Collections.IEnumerator)).Current)

    'Value collection
    Assert.AreEqual(data.Count, data.Values.Count)
    Assert.IsTrue(data.Values.IsReadOnly)
    Dim i As Integer = 0
    While i < sample.Count AndAlso i < 5
        Assert.IsTrue(data.Values.Contains(sample(i).Value))
        System.Math.Max(System.Threading.Interlocked.Increment(i),i - 1)
    End While

    Dim ev As IEnumerator(Of String) = data.Values.GetEnumerator()
    Assert.IsTrue(ev.MoveNext())
    Dim firstvalue As String = ev.Current
    Assert.IsTrue(ev.MoveNext())
    Assert.AreNotEqual(firstvalue, ev.Current)
    ev.Reset()
    Assert.IsTrue(ev.MoveNext())
    Assert.AreEqual(firstvalue, (DirectCast(ev, System.Collections.IEnumerator)).Current)
End Using