Add random_color and the color palette

random_color returns an immutable (red, green, blue) tuple of integers from 0 to 255
and random_palette_color picks a named color. Both take an optional random.Random
so that tests can seed them.

Task: MIL-003#1
Task: MIL-003#2

tests/test_colors.py

@@ -0,0 +1,53 @@
+import random
+
+from turtle_challenges.colors import random_color, random_palette_color
+from turtle_challenges.constants import (
+    COLOR_CHANNEL_MAX,
+    COLOR_CHANNEL_MIN,
+    COLOR_PALETTE,
+)
+
+
+def test_random_color_is_a_tuple_of_three_integers() -> None:
+    color = random_color(random.Random(1))
+
+    assert isinstance(color, tuple)
+    assert len(color) == 3
+    assert all(isinstance(channel, int) for channel in color)
+
+
+def test_random_color_channels_stay_in_range() -> None:
+    rng = random.Random(2)
+
+    for _ in range(500):
+        assert all(
+            COLOR_CHANNEL_MIN <= channel <= COLOR_CHANNEL_MAX
+            for channel in random_color(rng)
+        )
+
+
+def test_random_color_is_repeatable_with_the_same_seed() -> None:
+    first = [random_color(random.Random(7)) for _ in range(3)]
+    second = [random_color(random.Random(7)) for _ in range(3)]
+
+    assert first == second
+
+
+def test_random_color_varies_between_calls() -> None:
+    rng = random.Random(3)
+
+    assert len({random_color(rng) for _ in range(20)}) > 1
+
+
+def test_random_color_works_without_a_generator() -> None:
+    assert len(random_color()) == 3
+
+
+def test_random_palette_color_comes_from_the_palette() -> None:
+    rng = random.Random(4)
+
+    assert {random_palette_color(rng) for _ in range(100)} <= set(COLOR_PALETTE)
+
+
+def test_random_palette_color_works_without_a_generator() -> None:
+    assert random_palette_color() in COLOR_PALETTE

tests/test_constants.py

@@ -1,5 +1,14 @@
 from turtle_challenges import constants
 
 
+def test_color_mode_matches_the_largest_channel_value() -> None:
+    assert constants.COLOR_MODE == constants.COLOR_CHANNEL_MAX == 255
+
+
 def test_challenge_names_are_unique() -> None:
     assert len(set(constants.CHALLENGE_NAMES)) == len(constants.CHALLENGE_NAMES)
+
+
+def test_palette_has_only_non_empty_names() -> None:
+    assert constants.COLOR_PALETTE
+    assert all(name for name in constants.COLOR_PALETTE)