Public Overloads Sub CopyTo( _
   ByVal target As String, _
   ByVal replace As Boolean _
) 

public void CopyTo( 
   string target,
   bool replace
)

using(TempDirectory a = new TempDirectory())
using(TempDirectory b = new TempDirectory())
{
    File.WriteAllText(Path.Combine(a.TempPath, "a.txt"), "text-a");
    Directory.CreateDirectory(Path.Combine(a.TempPath, "child"));
    File.WriteAllText(Path.Combine(a.TempPath, @"child\b.txt"), "text-b");

    a.CopyTo(b.TempPath);
    Assert.IsTrue(File.Exists(Path.Combine(b.TempPath, "a.txt")));
    Assert.AreEqual("text-a", File.ReadAllText(Path.Combine(b.TempPath, "a.txt")));
    Assert.IsTrue(File.Exists(Path.Combine(b.TempPath, @"child\b.txt")));
    Assert.AreEqual("text-b", File.ReadAllText(Path.Combine(b.TempPath, @"child\b.txt")));

    File.WriteAllText(Path.Combine(a.TempPath, @"child\b.txt"), "text-b-new");
    a.CopyTo(b.TempPath, true);
    //has changed
    Assert.AreEqual("text-b-new", File.ReadAllText(Path.Combine(b.TempPath, @"child\b.txt")));
}

Using a As New TempDirectory()
    Using b As New TempDirectory()
        File.WriteAllText(Path.Combine(a.TempPath, "a.txt"), "text-a")
        Directory.CreateDirectory(Path.Combine(a.TempPath, "child"))
        File.WriteAllText(Path.Combine(a.TempPath, "child\b.txt"), "text-b")

        a.CopyTo(b.TempPath)
        Assert.IsTrue(File.Exists(Path.Combine(b.TempPath, "a.txt")))
        Assert.AreEqual("text-a", File.ReadAllText(Path.Combine(b.TempPath, "a.txt")))
        Assert.IsTrue(File.Exists(Path.Combine(b.TempPath, "child\b.txt")))
        Assert.AreEqual("text-b", File.ReadAllText(Path.Combine(b.TempPath, "child\b.txt")))

        File.WriteAllText(Path.Combine(a.TempPath, "child\b.txt"), "text-b-new")
        a.CopyTo(b.TempPath, True)
        'has changed
        Assert.AreEqual("text-b-new", File.ReadAllText(Path.Combine(b.TempPath, "child\b.txt")))
    End Using
End Using