Refactoring Trivia

Exercise based on the Trivia Legacy Code Retreat code.

Steps

Golden Master

• Capture the program's output and check whether it's deterministic or not;
• Repeat the execution a reasonable number of times, until the code coverage gives you enough confidence for your subsequent refactoring activities;
• Collect the output in a file, and include it in the test project, using an error-prone manual operation (Poka-yoke).

Make the output deterministic

Injecting pararameters via args

• Identify the source of non-determinism;
• Make it parametric and make the parameter controllable via args;
• Use parameters in tests to make them deterministic.

Via Slice

• Identify the source of non-determinism;
• Extract it as a method;
• Make the method virtual, so it can be overridden in the tests; using inheritance make a test version of the productive code, which removes the non-deterministic behaviors;
• When needed, introduce non-static classes and replace the static program entry point with a non-static method.

Via Peel

• Identify the source of non-determinism;
• Isolate it from the code, moving it to the top;
• Extract the rest of the code in a separate method, which takes the non-deterministic value as a parameter;
• Use the new method in the test, with a deterministic parameter.

Refactor Game's constructor: move question creation to a dedicated class

• Extract the business logic present in the constructor of Game to a separate method FillQuestions()
• Move FillQuestions() in a separate QuestionDeck class; Game's constructor will create an instance of QuestionDeck and will store it as an instance field;
• Pass FillQuestions() the current instance of Game so it can stil access the needed fields. We will move them later;
• To achieve the previous step, encapsulate all the fields FillQuestions() needs to access, creating Bottlenecks.
• FillQuestions() also accesses another Game's method, createRockQuestion(): move it to QuestionDeck as well;

Move CurrentCategory() to QuestionDeck

• We aim to move

private String currentCategory()
{
    if (places[currentPlayer] == 0) return "Pop";
    if (places[currentPlayer] == 4) return "Pop";
    if (places[currentPlayer] == 8) return "Pop";
    if (places[currentPlayer] == 1) return "Science";
    if (places[currentPlayer] == 5) return "Science";
    if (places[currentPlayer] == 9) return "Science";
    if (places[currentPlayer] == 2) return "Sports";
    if (places[currentPlayer] == 6) return "Sports";
    if (places[currentPlayer] == 10) return "Sports";
    return "Rock";
}

to QuestionDeck;

• First, make places[currentPlayer] a parameter to remove the duplication. To do so, create a Bottleneck for currentCategory extracting its body in a separate method;
• Then refactor places[currentPlayer] as a parameter;
• The resulting method won't contain any reference to places[currentPlayer], and won't have but 1 single usage (the original currentCategory()), since it's a bottleneck; move it to QuestionDeck

Move AskQuestion to QuestionDeck

• We aim to move

        private void askQuestion()
        {
            if (currentCategory() == "Pop")
            {
                Console.WriteLine(PopQuestions.First());
                PopQuestions.RemoveFirst();
            }
            if (currentCategory() == "Science")
            {
                Console.WriteLine(ScienceQuestions.First());
                ScienceQuestions.RemoveFirst();
            }
            if (currentCategory() == "Sports")
            {
                Console.WriteLine(SportsQuestions.First());
                SportsQuestions.RemoveFirst();
            }
            if (currentCategory() == "Rock")
            {
                Console.WriteLine(RockQuestions.First());
                RockQuestions.RemoveFirst();
            }
        }

to QuestionDeck

• Since there are multiple usages of QuestionDeck, first create a bottleneck using Extract Method, generating a separate AskQuestionCategory() method;
• Make currentCategory() one of its parameters with Extract Parameter;
• Use Move to move AskQuestionCategory() to QuestionDeck.

Move Game's fields to QuestionDeck

• We aim to move Game's fields to QuestionDeck
• First inject the Game instance into QuestionDeck through constructor instead of through methods; that's another way to create a bottleneck, since we end up with one single reference to Game;
• Now that there's one single reference to Game, move Game's fields to QuestionDeck, using Extract Field;
• Using Inline we can now remove all the references from Game.
• Remove the injection of the unused Game instance into QuestioDeck

Move Console.WriteLine() up from AskCategoryQuestion()

• We aim to remove the duplication of present in AskCategoryQuestion: there are multiple Console.WriteLine();
• Using ExtractMethod, Split declaration and assignment, Move to outer scope, Merge variables, Rename and Inline it's possible to move all the Console.WriteLine()s up in the caller method Game.askQuestion()
• Once AskCategoryQuestion() returns a string rather than writing to the console, it's easy to cover its behavior with unit tests.

Reuse CreateRockQuestion()

• Looking at FillQuestions()'s code it's apparent that there is a missing reuse of the code implemented by CreateRockQuestion()

public void FillQuestions()
{
    for (var i = 0; i < 50; i++)
    {
        _popQuestions.AddLast("Pop Question " + i);
        _scienceQuestions.AddLast(("Science Question " + i));
        _sportsQuestions.AddLast(("Sports Question " + i));
        _rockQuestions.AddLast(CreateRockQuestion(i));
    }
}
 public string CreateRockQuestion(int index)
{
    return "Rock Question " + index;
}

• Using Split string, Introduce parameter and "Rename" convert to the code

public void FillQuestions()
{
    for (var i = 0; i < 50; i++)
    {
        _popQuestions.AddLast(CreateQuestion(i, "Pop"));
        _scienceQuestions.AddLast(CreateQuestion(i, "Science"));
        _sportsQuestions.AddLast(CreateQuestion(i, "Sports"));
        _rockQuestions.AddLast(CreateQuestion(i, "Rock"));
    }
}
 public string CreateQuestion(int index, string category)
{
    return category + " Question " + index;
}