Diskette

I was emptying out a bunch of junk from my apartment and came across an old 3.5" floppy disk. My mind - being as it is - immediately wondered what the unit tests would look like if I were writing a virtual floppy disk (because nobody's got real floppy drives these days.)

On my Diskette class, I would expose the following methods to modify/access state:

• bool ToggleDiskAccessSlot()
  
• bool ToggleWriteProtect()
  
• void RotateDisk(int numSectors)
  
• int Read(int cylinder, int side)
  
• void Write(int cylinder, int side, int value)
  

Using Roy Osherove's naming strategy (a la accepted answer to this question), I'd add a unit test class named DisketteTests. Unit tests - IMHO - are intended to ensure that public methods modify the internal state of an object as expected. A test first sets up the object under test to a known state, then invokes a method, and finally makes an assertion about the state.

I might want to test the ability to read or write while the disk access slot is closed (I'd expect some exception to be thrown, so there's no explicit calls to Assert in the method body, the assertion is made by the test framework based on the test's custom attributes):

[ExpectedException(typeof(InvalidOperationException))]
[TestMethod]
public void Read_DiskAccessSlotIsClosed_ThrowsException()
{
    Diskette d = new Diskette();
    // intentionally missing the step to ToggleDiskAccessSlot();
    Ignore(d.Read(1, 1));
}

A more standard test might look like this:

[TestMethod]
public void Read_DiskAccessSlotIsOpen_GetsCurrentValue()
{
    Diskette d = new Diskette();
    if (!d.ToggleDiskAccessSlot())
    {
        Assert.Fail("Unable to open disk access slot");
    }
    int value = d.Read(1, 1);
    Assert.AreEqual(value, 0);
}