Serial port - no bytes available - vb.net

Question

I'm developing an app that takes bytes from COM port and manage them.
Unfortunately I don't have the opportunity to work on pc where this app will run, so I need a way to send "fake data" on my COM port so my app can read it.
Whatever I do, no bytes are available on selected COM port.
This is a basic sample:
'First I create and open desired COM port
Dim port = New SerialPort(cboPorts.SelectedItem, 9600, Parity.None, 8, StopBits.One)
port.Open()
If Not port.IsOpen Then Exit Sub
Then, with a timer, I try to write on it and then read:
Private Sub tmrTest_Tick(sender As Object, e As EventArgs) Handles tmrTest.Tick
Dim tot = rnd.Next(0, 3)
If tot > 0 Then
Dim buffer(tot) As Byte
rnd.NextBytes(buffer)
port.Write(buffer, 0, tot)
Dim t = port.BytesToRead
Console.WriteLine("Got {0} bytes on COM port", t)
End If
End Sub
In real app, bytes are not read right after they are written (I have a timer that reads COM port every second) but result is the same: port.BytesToRead is always zero.

Answer 1

Serial ports don't work this way. You can't read back the data you just wrote out. When you read, you you read the input buffer and when you write you write to the output buffer (you can't read the output buffer)
The only way to simulate what you want is to use another machine and connect a serial port between them, or read and write to two different serial ports on the same machine AppA writes to serial port 1 and reads from port 2 and AppB does the opposite.