Add the Scoreboard and the game over message

Task: MIL-006#1
Task: MIL-006#2
Task: MIL-006#3

tests/test_scoreboard.py

@@ -0,0 +1,36 @@
+"""@file test_scoreboard.py
+@brief Tests for the Scoreboard.
+"""
+
+from turtle import TurtleScreen
+
+from scoreboard import Scoreboard
+
+
+def test_level_starts_at_one(screen: TurtleScreen) -> None:
+    assert Scoreboard().level == 1
+
+
+def test_level_text_shows_level_one_at_start(screen: TurtleScreen) -> None:
+    assert Scoreboard().level_text == "Level: 1"
+
+
+def test_level_text_follows_level() -> None:
+    board = Scoreboard.__new__(Scoreboard)
+    board.level = 7
+    assert board.level_text == "Level: 7"
+
+
+def test_increase_level_adds_one(screen: TurtleScreen) -> None:
+    board = Scoreboard()
+    board.increase_level()
+    assert board.level == 2
+    assert board.level_text == "Level: 2"
+
+
+def test_game_over_keeps_level(screen: TurtleScreen) -> None:
+    board = Scoreboard()
+    board.increase_level()
+    board.game_over()
+    assert board.level == 2
+    assert board.position() == (0, 0)