Asynchronous TDD - Test Class blocks

How do I create a unit test to test a class that sits in a loop?

Here's the scenario.

I have a class that is injected with a reference to a serial port.

The class has a method called Send(String data);

This public method invokes an aysnchronous private method to do the actual work.

The class under test (CUT) should do the following when this method is called.

1) split the string into chars.
2) send a char
3) wait for the char to be echoed
4) send the next char (repeat until all chars sent)

So after sending the first char the CUT will sit in a loop waiting for an echo until it receives one or times out.

The problem I have that is once the CUT has entered this loop it will block the test class until it times out.

Since I need the test class to send the echo to the CUT im stuck.

To test this I've created a mock serial port and im using NUnit.

The test is below. The idea is that after sending the test string I wait for the CUT to respond. Each time the CUT writes a char to the serial port the wait is cancelled and I write an echo to the serial port and the CUT responds to this by sending the next char.

    [Test]
    public void Test()
    {
        _serialPort.DataSentEvent += new EventHandler(_serialPort_DataSentEvent);

        _completedSync = new ManualResetEvent(false);

        _wrapperPort.Send("TEST");

        _completedSync.WaitOne(1000); // wait for first char

        Assert.AreEqual("T", _serialPort.BufferOUT); //first char sent

        _serialPort.BufferIN = "T"; //write the echo

        _completedSync.WaitOne(1000); //wait for second char

        Assert.AreEqual("E", _serialPort.BufferOUT); //second char sent

        //...etc
    }

    void _serialPort_DataSentEvent(object sender, EventArgs e)
    {
        _completedSync.Set();
    }

But what happens is the CUT blocks as soon as Send("TEST") is called and control only returns to the test class once the CUT has timed out waiting for an echo.

Since the Send method is being completed on another thread why is it blocking the test class?

ansaurus

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Asynchronous TDD - Test Class blocks

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