Question

I have a class method that looks like this:

private List<string> DataStoreContents = new List<string>(new[] { "", "", "", "" });

public void InputDataStore(int DataStore, string Data)
{
  DataStoreContents[DataStore - 1] = Data;
}

I want to make sure that DataStore is >=1 and <= 4

How can I write a unit test that ensures that?

Answer 1

Either

Assert.IsTrue(DataStore >= 1 && DataStore <= 4);

or, if you prefer the fluent interface

Assert.That(DataStore, Is.GreaterThanOrEqualTo(1).And.LessThanOrEqualTo(4));

[EDIT – in response to you clarification above]

It sounds like you want to have some sort of barrier checking to check that the supplied values are in range.

In this case, you have a few choices:

Philip Fourie has given an answer involving code contracts.

Another simple approach is to write the barrier check yourself:

public void InputDataStore(int DataStore, string Data)
{
    if (DataStore < 1 || DataStore > 4)
    {
        throw new ArgumentOutOfRangeException("DataStore", "Must be in the range 1-4 inc.");
    }
    DataStoreContents[DataStore - 1] = Data;
}

If you don’t want to throw an exception, but maybe want to log it and exit cleanly:

public void InputDataStore(int DataStore, string Data)
{
    if (DataStore < 1 || DataStore > 4)
    {
        // log something here and then return
        return;
    }
    DataStoreContents[DataStore - 1] = Data;
}

To link back to unit testing. A unit test, for example, could be a test you write to check that when InputDataStore is called with a value that is out of range, that it throws an expcetion. Another would be that when it is called with a value in range, it doesn’t throw an exception, and it updates DataStoreContents correctly.