Adopt the Food class and its tests

Copied unchanged from the base: class Food(Turtle) with refresh, and one random_coordinate function that the tests replace. MIL-003 checks the values against the day-21 lectures.

Task: MIL-002#3
Closes #10

tests/test_food.py

@@ -0,0 +1,77 @@
+"""Tests of the food, with a fake `Turtle` as its base class."""
+
+import importlib
+import sys
+
+import pytest
+
+from fakes import install_fake_turtle, make_food, script_randint
+from snake_game import constants
+
+
+def test_food_is_a_blue_half_size_circle_with_the_pen_up_and_no_animation(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    food = make_food(monkeypatch)
+
+    assert ("shape", ("circle",)) in food.calls
+    assert ("shapesize", (0.5, 0.5)) in food.calls
+    assert ("color", ("blue",)) in food.calls
+    assert ("speed", ("fastest",)) in food.calls
+    assert "penup" in food.call_names()
+
+
+def test_food_inherits_from_turtle_and_calls_the_base_class_first(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    install_fake_turtle(monkeypatch)
+    module = importlib.import_module("snake_game.food")
+
+    food = module.Food()
+
+    assert issubclass(module.Food, sys.modules["turtle"].Turtle)
+    assert food.calls[0][0] == "shape"  # the base class set up `calls` before
+
+
+def test_food_starts_at_a_random_place(monkeypatch: pytest.MonkeyPatch) -> None:
+    script_randint(monkeypatch, [12, -34])
+
+    food = make_food(monkeypatch)
+
+    assert food.position() == (12, -34)
+
+
+def test_refresh_moves_the_food_to_a_new_random_place(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    script_randint(monkeypatch, [1, 2, 3, 4])
+    food = make_food(monkeypatch)
+
+    food.refresh()
+
+    assert food.position() == (3, 4)
+
+
+def test_random_coordinate_asks_for_a_number_from_wall_to_wall(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    bounds = script_randint(monkeypatch, [7])
+    install_fake_turtle(monkeypatch)
+    module = importlib.import_module("snake_game.food")
+
+    result = module.random_coordinate()
+
+    assert result == 7
+    assert bounds == [(-constants.WALL_LIMIT, constants.WALL_LIMIT)]
+
+
+def test_random_places_are_always_inside_the_walls(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    install_fake_turtle(monkeypatch)
+    module = importlib.import_module("snake_game.food")
+
+    places = [module.random_coordinate() for _ in range(500)]
+
+    wall = constants.WALL_LIMIT
+    assert all(-wall <= place <= wall for place in places)