Add the Player class and the Up key binding

Task: MIL-003#1
Task: MIL-003#2
Task: MIL-003#3

tests/conftest.py

@@ -0,0 +1,18 @@
+"""Shared fixtures. Tests that need a window skip when no display is available."""
+
+import tkinter
+import turtle
+
+import pytest
+
+
+@pytest.fixture(scope="session")
+def screen() -> turtle.TurtleScreen:
+    """A single hidden turtle screen shared by the tests that draw."""
+    try:
+        game_screen = turtle.Screen()
+    except tkinter.TclError:
+        pytest.skip("no display available")
+    game_screen.tracer(0)
+    game_screen.getcanvas().winfo_toplevel().withdraw()
+    return game_screen

tests/test_player.py

@@ -0,0 +1,33 @@
+"""Tests for the Player class (need a display; skipped without one)."""
+
+import pytest
+
+from constants import MOVE_DISTANCE, STARTING_POSITION
+from player import Player
+
+
+@pytest.fixture
+def player(screen) -> Player:
+    new_player = Player()
+    yield new_player
+    new_player.hideturtle()
+
+
+def test_player_starts_at_starting_position(player: Player) -> None:
+    assert player.position() == STARTING_POSITION
+
+
+def test_player_faces_north(player: Player) -> None:
+    assert player.heading() == 90
+
+
+def test_go_up_moves_forward_by_move_distance(player: Player) -> None:
+    start_y = player.ycor()
+    player.go_up()
+    assert player.ycor() == start_y + MOVE_DISTANCE
+
+
+def test_go_up_never_moves_sideways(player: Player) -> None:
+    for _ in range(5):
+        player.go_up()
+    assert player.xcor() == pytest.approx(STARTING_POSITION[0])