Adopt the test fakes
Copied unchanged from the base (020-snake-game, commit 1a638c9): the fake segment, the fake screen and the fake Turtle base class that record their calls, so every test runs without a display. The fake turtle module is installed with monkeypatch, so it is undone after each test. Task: MIL-002#1 Closes #8
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"""Fakes that stand in for turtles and the screen, so that no test opens a window."""
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import importlib
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import math
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import os
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import subprocess
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import sys
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import types
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from collections.abc import Callable, Sequence
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from pathlib import Path
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from typing import Any
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import pytest
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from snake_game.snake import Snake
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SRC = Path(__file__).resolve().parents[1] / "src"
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# Modules whose classes inherit from `Turtle`: they bind their base class when they
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# are imported, so each test that installs the fake `turtle` module imports them anew.
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INHERITING_MODULES = ("snake_game.food", "snake_game.scoreboard")
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class FakeTerminatorError(Exception):
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"""Stands in for `turtle.Terminator`."""
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class FakeTclError(Exception):
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"""Stands in for `tkinter.TclError`."""
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class FakeSegment:
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"""A turtle that records what is done to it, in order, and keeps its state.
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It is a segment of the snake, and also the base class that stands in for
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`turtle.Turtle` when `Food` and `Scoreboard` are tested.
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"""
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def __init__(self) -> None:
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self.calls: list[tuple[str, tuple[object, ...]]] = []
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self.x = 0.0
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self.y = 0.0
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self.angle = 0.0
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def shape(self, name: str, /) -> None:
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self.calls.append(("shape", (name,)))
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def shapesize(self, stretch_wid: float, stretch_len: float) -> None:
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self.calls.append(("shapesize", (stretch_wid, stretch_len)))
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def color(self, color: str, /) -> None:
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self.calls.append(("color", (color,)))
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def speed(self, speed: str) -> None:
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self.calls.append(("speed", (speed,)))
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def penup(self) -> None:
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self.calls.append(("penup", ()))
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def hideturtle(self) -> None:
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self.calls.append(("hideturtle", ()))
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def clear(self) -> None:
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self.calls.append(("clear", ()))
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def write(
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self,
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arg: str,
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align: str = "left",
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font: tuple[str, int, str] = ("Arial", 8, "normal"),
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) -> None:
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self.calls.append(("write", (arg, align, font)))
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def goto(self, x: float | tuple[float, float], y: float | None = None, /) -> None:
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if isinstance(x, tuple):
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x, y = x
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assert y is not None
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self.calls.append(("goto", (x, y)))
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self.x, self.y = x, y
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def xcor(self) -> float:
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return self.x
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def ycor(self) -> float:
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return self.y
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def position(self) -> tuple[float, float]:
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return (self.x, self.y)
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def distance(self, x: tuple[float, float], /) -> float:
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return math.hypot(self.x - x[0], self.y - x[1])
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def forward(self, distance: float, /) -> None:
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self.calls.append(("forward", (distance,)))
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radians = math.radians(self.angle)
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self.x += round(distance * math.cos(radians), 10)
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self.y += round(distance * math.sin(radians), 10)
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def heading(self) -> float:
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return self.angle
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def setheading(self, to_angle: float, /) -> None:
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self.calls.append(("setheading", (to_angle,)))
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self.angle = float(to_angle) % 360
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def call_names(self) -> list[str]:
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"""Return the names of the calls, in the order they were made."""
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return [name for name, _ in self.calls]
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class FakeFood:
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"""A food that counts how often it was moved."""
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def __init__(self, x: float, y: float) -> None:
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self.x = x
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self.y = y
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self.refreshes = 0
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def refresh(self) -> None:
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self.refreshes += 1
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def position(self) -> tuple[float, float]:
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return (self.x, self.y)
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class FakeScoreboard:
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"""A scoreboard that counts how often the score was raised."""
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def __init__(self) -> None:
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self.increases = 0
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self.game_overs = 0
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def increase_score(self) -> None:
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self.increases += 1
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def game_over(self) -> None:
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self.game_overs += 1
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class FakeScreen:
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"""A screen that records what is done to it, in order.
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After `frames_before_close` updates it behaves like a closed window: the next
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`update` raises `closing_error`.
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"""
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def __init__(
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self,
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frames_before_close: int = 0,
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closing_error: type[Exception] = FakeTerminatorError,
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) -> None:
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self.calls: list[tuple[str, tuple[object, ...]]] = []
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self.bindings: dict[str, Callable[[], object]] = {}
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self._updates_left = frames_before_close
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self._closing_error = closing_error
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def setup(self, width: float, height: float) -> None:
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self.calls.append(("setup", (width, height)))
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def bgcolor(self, color: str, /) -> None:
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self.calls.append(("bgcolor", (color,)))
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def title(self, titlestring: str, /) -> None:
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self.calls.append(("title", (titlestring,)))
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def tracer(self, n: int, /) -> None:
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self.calls.append(("tracer", (n,)))
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def listen(self) -> None:
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self.calls.append(("listen", ()))
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def onkey(self, fun: Callable[[], object], key: str) -> None:
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self.calls.append(("onkey", (key,)))
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self.bindings[key] = fun
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def update(self) -> None:
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self.calls.append(("update", ()))
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if self._updates_left == 0:
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raise self._closing_error
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self._updates_left -= 1
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def exitonclick(self) -> None:
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self.calls.append(("exitonclick", ()))
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def call_names(self) -> list[str]:
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"""Return the names of the calls, in the order they were made."""
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return [name for name, _ in self.calls]
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def make_snake() -> tuple[Snake, list[FakeSegment]]:
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"""Make a snake whose segments are fakes, and return the fakes too."""
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created: list[FakeSegment] = []
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def factory() -> FakeSegment:
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segment = FakeSegment()
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created.append(segment)
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return segment
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return Snake(segment_factory=factory), created
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def install_fake_turtle(
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monkeypatch: pytest.MonkeyPatch,
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*,
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frames_before_close: int = 0,
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closing_error: type[Exception] = FakeTerminatorError,
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) -> tuple[list[FakeSegment], list[FakeScreen]]:
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"""Replace the `turtle` and `tkinter` modules with fakes for one test.
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The fake screen acts like a window that the player closes after
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`frames_before_close` updates, by raising `closing_error` from `update`.
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Every turtle the code under test creates, including a `Food` or a `Scoreboard`
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whose base class is the fake `Turtle`, is added to the first list returned;
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every screen is added to the second. `food` and `scoreboard` are forgotten, so
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that they are imported again against the fake and removed again after the test.
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"""
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segments: list[FakeSegment] = []
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screens: list[FakeScreen] = []
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class RegisteredSegment(FakeSegment):
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def __init__(self) -> None:
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super().__init__()
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segments.append(self)
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def make_screen() -> FakeScreen:
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screen = FakeScreen(frames_before_close, closing_error)
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screens.append(screen)
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return screen
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turtle_module = types.ModuleType("turtle")
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turtle_module.__dict__["Turtle"] = RegisteredSegment
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turtle_module.__dict__["Screen"] = make_screen
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turtle_module.__dict__["Terminator"] = FakeTerminatorError
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tkinter_module = types.ModuleType("tkinter")
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tkinter_module.__dict__["TclError"] = FakeTclError
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monkeypatch.setitem(sys.modules, "turtle", turtle_module)
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monkeypatch.setitem(sys.modules, "tkinter", tkinter_module)
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for name in INHERITING_MODULES:
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# Set, then delete: when the test ends monkeypatch undoes both in reverse
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# order and the key is gone again, whatever the test imported meanwhile.
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monkeypatch.setitem(sys.modules, name, types.ModuleType(name))
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monkeypatch.delitem(sys.modules, name)
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return segments, screens
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def script_randint(
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monkeypatch: pytest.MonkeyPatch, values: Sequence[int]
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) -> list[tuple[int, int]]:
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"""Make `random.randint` return the given values in turn, then the upper bound.
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Returns the list that collects the bounds of every call.
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"""
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queue = iter(values)
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bounds: list[tuple[int, int]] = []
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def fake_randint(low: int, high: int) -> int:
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bounds.append((low, high))
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return next(queue, high)
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monkeypatch.setattr("random.randint", fake_randint)
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return bounds
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def make_food(monkeypatch: pytest.MonkeyPatch) -> Any:
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"""Make a real `Food` whose base class is the fake `Turtle`.
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The result is typed `Any` because it has the methods of `Food` (`refresh`) and
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the recording methods of the fake base class (`calls`, `position`) at once.
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"""
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install_fake_turtle(monkeypatch)
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module = importlib.import_module("snake_game.food")
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return module.Food()
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def make_scoreboard(monkeypatch: pytest.MonkeyPatch) -> Any:
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"""Make a real `Scoreboard` whose base class is the fake `Turtle`.
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The result is typed `Any` because it has the methods of `Scoreboard`
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(`increase_score`) and the recording methods of the fake base class (`calls`)
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at once.
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"""
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install_fake_turtle(monkeypatch)
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module = importlib.import_module("snake_game.scoreboard")
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return module.Scoreboard()
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def imports_turtle_or_tkinter(module_name: str) -> bool:
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"""Tell whether importing a module in a fresh interpreter loads a display module."""
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code = (
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f"import sys, {module_name}; "
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"print('turtle' in sys.modules or 'tkinter' in sys.modules)"
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)
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result = subprocess.run(
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[sys.executable, "-c", code],
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env={**os.environ, "PYTHONPATH": str(SRC)},
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capture_output=True,
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text=True,
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check=False,
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)
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assert result.returncode == 0, result.stderr
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return result.stdout.strip() == "True"
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