Tennis Refactoring

Level: Intermediate 30–60 min

Concepts: RefactoringLegacy CodeStrings

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You are given a working tennis scoring function. The code is correct but hard to read. Your job is to refactor it into something clean — without breaking existing behavior.

This is a refactoring kata. Write characterization tests first, then improve the code.

Tennis Scoring Rules

• A game starts at 0-0 (called “Love-All”)
• Scores go: 0 (“Love”), 1 (“Fifteen”), 2 (“Thirty”), 3 (“Forty”)
• If both players have 40, it’s “Deuce”
• If the score is Deuce and a player scores, they have “Advantage”
• If the player with Advantage scores again, they win
• If the other player scores when their opponent has Advantage, it goes back to Deuce

The Legacy Code

function getScore(p1Score, p2Score, p1Name, p2Name) {
  var result = "";
  if (p1Score == p2Score) {
    if (p1Score == 0) result = "Love-All";
    else if (p1Score == 1) result = "Fifteen-All";
    else if (p1Score == 2) result = "Thirty-All";
    else if (p1Score >= 3) result = "Deuce";
  } else if (p1Score >= 4 || p2Score >= 4) {
    var diff = p1Score - p2Score;
    if (diff == 1) result = "Advantage " + p1Name;
    else if (diff == -1) result = "Advantage " + p2Name;
    else if (diff >= 2) result = "Win for " + p1Name;
    else if (diff <= -2) result = "Win for " + p2Name;
  } else {
    var scores = ["Love", "Fifteen", "Thirty", "Forty"];
    result = scores[p1Score] + "-" + scores[p2Score];
  }
  return result;
}

Your Task

Step 1: Write characterization tests. Cover every scoring combination. Your tests should capture the exact behavior of the current code.

Step 2: Refactor. Improve readability, extract concepts, remove duplication. Keep all tests green throughout.

Test Cases

Player 1 Score	Player 2 Score	Output
0	0	Love-All
1	1	Fifteen-All
2	2	Thirty-All
3	3	Deuce
4	4	Deuce
1	0	Fifteen-Love
0	1	Love-Fifteen
2	1	Thirty-Fifteen
3	1	Forty-Fifteen
4	3	Advantage Player1
3	4	Advantage Player2
5	4	Advantage Player1
5	3	Win for Player1
3	5	Win for Player2

Bonus

• Refactor to use polymorphism — replace conditionals with a scoring strategy per game state
• Add a TennisGame class that tracks points via wonPoint(playerName) and reports score via getScore()
• Support tiebreak scoring (numeric, first to 7, win by 2)

Hint

The code has three distinct states: equal scores, endgame (scores ≥ 40), and normal play. Each state has different formatting rules. Extracting these into named methods or separate functions makes the logic immediately clearer.