Establishing the API

Creating the WordReplacer Class

The next step is to formalize the functionality of the application by establishing its API. The informal requirements for the application are as follows:

The application must accept as input a sentence containing token placeholders for parts of speech, and output a new sentence with the tokens replaced with randomized words corresponding to the part of speech.

An example run might look like this:

Enter a sentence: The [adjective] [noun] [verb].
The slow chicken dances.

We can manage this with one class containing a single public method: WordReplacer.Replace.

Let's create the new class for this functionality. Be sure to put this class in the WordSub.App directory.

public class WordReplacer
{
    public string Replace(string text)
    {
        throw new NotImplementedException();
    }
}

As a placeholder, we will throw a NotImplementedException, so that anyone trying to call this method while it is under development will be met with a clear error message.

Calling the New Class

Now we can call this method from the Program.cs file:

var wordReplacer = new WordReplacer();
var result = wordReplacer.Replace("The [adjective] [noun] [verb].");
Console.WriteLine(result);

The file structure should now look like this:

word-sub/
└── WordSub.App
    ├── Program.cs
    ├── WordReplacer.cs
    └── WordSub.App.csproj

If you run the program now you will see the NotImplementedException error.

Success! We have a starter shell in place for the application. Just creating a minimal working program is the first milestone in building the solution.

Garbage In, Garbage Out

The requirements that we have provided are very lax. In reality we would want to define behavior in more detail. For example: What tense should be used? What do we do if we hit a token placeholder without a valid identifier? Should we allow duplicate replacement words?

Without proper requirements, we don't know if we have met acceptance criteria and cannot properly confirm that the system works through testing.