feat:add Snake Water Gun game with unit test

Author: yv256

games/snake_water_gun.py

@@ -0,0 +1,103 @@
+"""
+Snake Water Gun Game
+=====================
+
+A simple command-line game similar to Rock-Paper-Scissors.
+Choices: Snake, Water, Gun.
+
+Rules:
+    - Snake drinks Water  → Snake wins.
+    - Water damages Gun   → Water wins.
+    - Gun kills Snake     → Gun wins.
+    - Same choice         → Tie.
+
+Functions:
+    play(player_choice: str) -> str
+        Play a single round against the computer.
+    main() -> None
+        Run an interactive game loop until the user quits.
+"""
+
+import random
+import sys
+from typing import NoReturn
+
+
+VALID_CHOICES = ("Snake", "Water", "Gun")
+
+WIN_CONDITIONS = {
+    "Snake": "Water",  # Snake drinks Water
+    "Water": "Gun",    # Water damages Gun
+    "Gun": "Snake",    # Gun kills Snake
+}
+
+
+def play(player_choice: str) -> str:
+    """
+    Play one round of Snake Water Gun against the computer.
+
+    The function normalises the player's input (case-insensitive) and
+    validates it.  The computer picks a random choice.  It then
+    determines the winner according to the rules and returns a
+    descriptive string.
+
+    Args:
+        player_choice: The player's selection.  Any casing is accepted
+            ("snake", "SNAKE", "Snake", etc.).
+
+    Returns:
+        A string in one of the following formats:
+            - "You chose Snake, Computer chose Water. You win!"
+            - "You chose Water, Computer chose Gun. You lose!"
+            - "You chose Gun, Computer chose Gun. It's a tie!"
+            - "Invalid choice: <input>. Please choose Snake, Water, or Gun."
+
+    Examples:
+        >>> play("Snake")
+        'You chose Snake, Computer chose Water. You win!'   # if computer picks Water
+    """
+    # Normalise input: strip whitespace, capitalise first letter only
+    normalised = player_choice.strip().lower().capitalize()
+
+    if normalised not in VALID_CHOICES:
+        return (
+            f"Invalid choice: {player_choice}. "
+            f"Please choose {', '.join(VALID_CHOICES)}."
+        )
+
+    computer_choice = random.choice(VALID_CHOICES)
+
+    if normalised == computer_choice:
+        result = "It's a tie!"
+    elif WIN_CONDITIONS[normalised] == computer_choice:
+        result = "You win!"
+    else:
+        result = "You lose!"
+
+    return f"You chose {normalised}, Computer chose {computer_choice}. {result}"
+
+
+def main() -> None:
+    """
+    Run the interactive Snake Water Gun game loop.
+
+    The user is repeatedly prompted for a choice until they type
+    ``quit`` (case-insensitive).  Each round's result is printed
+    immediately.
+    """
+    print("Welcome to Snake Water Gun!")
+    print(f"Choices: {', '.join(VALID_CHOICES)}")
+    print("Enter 'quit' to exit.\n")
+
+    while True:
+        user_input = input("Your choice: ").strip()
+        if user_input.lower() == "quit":
+            print("Thanks for playing. Goodbye!")
+            break
+        result = play(user_input)
+        print(result)
+        print()
+
+
+if __name__ == "__main__":
+    main()

tests/games/test_snake_water_gun.py

@@ -0,0 +1,124 @@
+"""
+Unit tests for the Snake Water Gun game.
+
+Tests cover:
+    - All win/loss/tie combinations (3×3 matrix).
+    - Case‑insensitivity and whitespace handling.
+    - Invalid inputs.
+    - The interactive ``main()`` loop (with mocked I/O).
+"""
+
+import random
+import pytest
+from io import StringIO
+
+from snake_water_gun import play, main, VALID_CHOICES, WIN_CONDITIONS
+
+
+# ---------------------------------------------------------------------------
+# Helper: parametrised tests for play()
+# ---------------------------------------------------------------------------
+
+# Map computer choice to expected outcome for a given player choice
+OUTCOMES = {
+    # player chooses Snake
+    ("Snake", "Snake"): "It's a tie!",
+    ("Snake", "Water"): "You win!",
+    ("Snake", "Gun"): "You lose!",
+    # player chooses Water
+    ("Water", "Snake"): "You lose!",
+    ("Water", "Water"): "It's a tie!",
+    ("Water", "Gun"): "You win!",
+    # player chooses Gun
+    ("Gun", "Snake"): "You win!",
+    ("Gun", "Water"): "You lose!",
+    ("Gun", "Gun"): "It's a tie!",
+}
+
+
+@pytest.mark.parametrize(
+    "player_choice, computer_choice",
+    [
+        (p, c)
+        for p in VALID_CHOICES
+        for c in VALID_CHOICES
+    ],
+)
+def test_all_outcomes(player_choice: str, computer_choice: str, monkeypatch) -> None:
+    """
+    Verify that every possible combination returns the correct result string.
+    """
+    monkeypatch.setattr(random, "choice", lambda _: computer_choice)
+
+    result = play(player_choice)
+    expected_outcome = OUTCOMES[(player_choice, computer_choice)]
+    expected = (
+        f"You chose {player_choice}, Computer chose {computer_choice}. "
+        f"{expected_outcome}"
+    )
+    assert result == expected
+
+
+@pytest.mark.parametrize(
+    "raw_input, normalised",
+    [
+        ("snake", "Snake"),
+        ("SNAKE", "Snake"),
+        ("  water  ", "Water"),
+        ("GuN", "Gun"),
+    ],
+)
+def test_case_insensitivity_and_whitespace(
+    raw_input: str, normalised: str, monkeypatch
+) -> None:
+    """Input is normalised regardless of casing and surrounding spaces."""
+    # Fix computer choice to something predictable
+    monkeypatch.setattr(random, "choice", lambda _: "Gun")
+
+    result = play(raw_input)
+    # We expect the result string to contain the normalised player choice
+    assert f"You chose {normalised}" in result
+
+
+@pytest.mark.parametrize(
+    "invalid_input",
+    [
+        "",
+        "  ",
+        "rock",
+        "paper",
+        "scissors",
+        "snakes",
+        "gunwater",
+        "123",
+    ],
+)
+def test_invalid_input_returns_error(invalid_input: str) -> None:
+    """Invalid choices produce an error message."""
+    result = play(invalid_input)
+    assert result.startswith("Invalid choice:")
+
+
+# ---------------------------------------------------------------------------
+# Tests for main() interactive loop
+# ---------------------------------------------------------------------------
+
+def test_main_quit_immediately(monkeypatch, capsys) -> None:
+    """Typing 'quit' right away exits the loop with a goodbye message."""
+    monkeypatch.setattr("sys.stdin", StringIO("quit\n"))
+    main()
+    captured = capsys.readouterr()
+    assert "Thanks for playing. Goodbye!" in captured.out
+
+
+def test_main_one_round_then_quit(monkeypatch, capsys) -> None:
+    """Play a single round and then quit."""
+    inputs = StringIO("Snake\nquit\n")
+    monkeypatch.setattr("sys.stdin", inputs)
+    # Force computer choice to make assertion deterministic
+    monkeypatch.setattr(random, "choice", lambda _: "Water")
+
+    main()
+    captured = capsys.readouterr()
+    assert "You chose Snake, Computer chose Water. You win!" in captured.out
+    assert "Thanks for playing. Goodbye!" in captured.out