Add draw_shape and draw_shapes with tests

draw_shape turns 360 divided by the number of sides after each side and rejects
fewer than 3 sides. draw_shapes draws a triangle up to a decagon, each in a color
from the palette.

Task: MIL-003#3
Task: MIL-003#4
Task: MIL-003#5

tests/test_shapes.py

@@ -0,0 +1,94 @@
+import random
+
+import pytest
+
+from tests.fakes import FakePen
+from turtle_challenges.constants import (
+    COLOR_PALETTE,
+    FULL_TURN_DEGREES,
+    MAX_POLYGON_SIDES,
+    MIN_POLYGON_SIDES,
+    POLYGON_SIDE_LENGTH,
+)
+from turtle_challenges.shapes import draw_shape, draw_shapes
+
+SIDE_COUNTS = range(MIN_POLYGON_SIDES, MAX_POLYGON_SIDES + 1)
+
+
+@pytest.mark.parametrize("num_sides", SIDE_COUNTS)
+def test_draw_shape_draws_every_side_at_the_default_length(num_sides: int) -> None:
+    pen = FakePen()
+
+    draw_shape(pen, num_sides)
+
+    assert pen.args_of("forward") == [(POLYGON_SIDE_LENGTH,)] * num_sides
+
+
+@pytest.mark.parametrize("num_sides", SIDE_COUNTS)
+def test_draw_shape_turns_a_full_lap_in_equal_steps(num_sides: int) -> None:
+    pen = FakePen()
+
+    draw_shape(pen, num_sides)
+
+    expected_angle = FULL_TURN_DEGREES / num_sides
+    assert pen.args_of("right") == [(expected_angle,)] * num_sides
+
+
+def test_draw_shape_turns_72_degrees_for_a_pentagon() -> None:
+    pen = FakePen()
+
+    draw_shape(pen, 5)
+
+    assert pen.args_of("right")[0] == (72,)
+
+
+def test_draw_shape_uses_the_given_side_length() -> None:
+    pen = FakePen()
+
+    draw_shape(pen, 3, side_length=25)
+
+    assert pen.args_of("forward") == [(25,)] * 3
+
+
+@pytest.mark.parametrize("num_sides", [-1, 0, 1, 2])
+def test_draw_shape_rejects_fewer_than_three_sides(num_sides: int) -> None:
+    pen = FakePen()
+
+    with pytest.raises(ValueError, match="num_sides"):
+        draw_shape(pen, num_sides)
+
+    assert pen.calls == []
+
+
+def test_draw_shape_rejects_a_side_that_is_not_positive() -> None:
+    pen = FakePen()
+
+    with pytest.raises(ValueError, match="side_length"):
+        draw_shape(pen, 4, side_length=0)
+
+
+def test_draw_shapes_draws_a_triangle_up_to_a_decagon() -> None:
+    pen = FakePen()
+
+    draw_shapes(pen, random.Random(5))
+
+    assert len(pen.args_of("forward")) == sum(SIDE_COUNTS)
+    assert len(pen.args_of("color")) == len(SIDE_COUNTS)
+
+
+def test_draw_shapes_sets_a_palette_color_before_each_shape() -> None:
+    pen = FakePen()
+
+    draw_shapes(pen, random.Random(6))
+
+    colors = [args[0] for args in pen.args_of("color")]
+    assert all(color in COLOR_PALETTE for color in colors)
+    assert pen.names()[0] == "color"
+
+
+def test_draw_shapes_works_without_a_generator() -> None:
+    pen = FakePen()
+
+    draw_shapes(pen)
+
+    assert len(pen.args_of("color")) == len(SIDE_COUNTS)