Refactor coin toss game logic to improve structure and testability; add PlayGame function and corresponding tests

Author: chrisreddington

cmd/cointoss.go

@@ -3,7 +3,6 @@ package cmd
 import (
 	"fmt"
 	"os"
-	"strings"
 
 	"github.com/chrisreddington/gh-game/internal/cointoss"
 	userPrompt "github.com/cli/go-gh/v2/pkg/prompter"
@@ -21,24 +20,11 @@ var cointossCmd = &cobra.Command{
 		return cointoss.ValidateGuess(args[0])
 	},
 	Run: func(cmd *cobra.Command, args []string) {
-		game := cointoss.NewGame()
-		prompter := userPrompt.New(os.Stdin, os.Stdout, os.Stderr)
-		guess := strings.ToLower(strings.TrimSpace(args[0]))
-		streak := 0
-		keepPlaying := true
-
-		for keepPlaying {
-			game.Play(guess)
-			fmt.Println(game.GetResult())
-
-			if game.PlayerGuess == game.Result {
-				streak++
-				fmt.Printf("Streak: %d\n", streak)
-				guess, keepPlaying = cointoss.GetPlayerGuess(prompter)
-			} else {
-				fmt.Printf("Game Over! Final streak: %d\n", streak)
-				keepPlaying = false
-			}
-		}
+		input := userPrompt.New(os.Stdin, os.Stdout, os.Stderr)
+		cointoss.PlayGame(input, args[0])
 	},
 }
+
+func init() {
+	rootCmd.AddCommand(cointossCmd)
+}

internal/cointoss/cointoss.go

@@ -25,7 +25,8 @@ func NewGame() *Game {
 	}
 }
 
-func TossCoin() string {
+// TossCoin is a variable so it can be replaced in tests
+var TossCoin = func() string {
 	rand.Seed(time.Now().UnixNano())
 	if rand.Float32() < 0.5 {
 		return "heads"
@@ -73,3 +74,25 @@ func (g *Game) GetResult() string {
 	}
 	return fmt.Sprintf("You guessed %s but the coin landed on %s. You lose!", g.PlayerGuess, g.Result)
 }
+
+// PlayGame handles the main game loop
+func PlayGame(p prompter, initialGuess string) {
+	game := NewGame()
+	streak := 0
+	keepPlaying := true
+	guess := strings.ToLower(strings.TrimSpace(initialGuess))
+
+	for keepPlaying {
+		game.Play(guess)
+		fmt.Println(game.GetResult())
+		
+		if game.PlayerGuess == game.Result {
+			streak++
+			fmt.Printf("Streak: %d\n", streak)
+			guess, keepPlaying = GetPlayerGuess(p)
+		} else {
+			fmt.Printf("Game Over! Final streak: %d\n", streak)
+			keepPlaying = false
+		}
+	}
+}

internal/cointoss/cointoss_test.go

@@ -175,3 +175,54 @@ func TestGame_GetResult(t *testing.T) {
 func contains(s, substr string) bool {
 	return strings.Contains(s, substr)
 }
+
+func TestPlayGame(t *testing.T) {
+	tests := []struct {
+		name         string
+		selectAnswer int
+		selectError  error
+		initialGuess string
+		results      []string // sequence of coin flip results to test
+	}{
+		{
+			name:         "win first round then quit",
+			selectAnswer: 2, // quit
+			initialGuess: "heads",
+			results:      []string{"heads"},
+		},
+		{
+			name:         "lose first round",
+			initialGuess: "heads",
+			results:      []string{"tails"},
+		},
+		{
+			name:         "win twice then lose",
+			selectAnswer: 0, // heads
+			initialGuess: "heads",
+			results:      []string{"heads", "heads", "tails"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mockP := &mockPrompter{
+				selectAnswer: tt.selectAnswer,
+				selectError:  tt.selectError,
+			}
+
+			// Override TossCoin for deterministic testing
+			resultIndex := 0
+			oldTossCoin := TossCoin
+			TossCoin = func() string {
+				result := tt.results[resultIndex]
+				if resultIndex < len(tt.results)-1 {
+					resultIndex++
+				}
+				return result
+			}
+			defer func() { TossCoin = oldTossCoin }()
+
+			PlayGame(mockP, tt.initialGuess)
+		})
+	}
+}