Resolve pending commit link for RC-018

BuyStrategy with a pure buy-all plan, validated --interval, --buy-all,
a five attempt retry for reads that go stale (found in a real run), the
comparison of two batches of 300 s container runs and the screenshot of
lecture step 5. Code review RC-018.

Closes #26
Closes #27
Closes #28

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

docs/artifact-registry.md

@@ -16,7 +16,7 @@ document of a type. `Primary File` may contain a glob (e.g.
 | PP | Project Plan | docs/project-plan.md | 002 |
 | MIL | Milestone / Gateway | docs/milestones/*.md | 008 |
 | ADR | Architecture Decision Record | docs/adr/adr-NNNN-*.md | 0004 |
-| RC | SQA Review Record | docs/sqa/reviews/rc-*.md | 018 |
+| RC | SQA Review Record | docs/sqa/reviews/rc-*.md | 019 |
 | TM | Traceability Matrix | docs/sqa/traceability-matrix.md | 002 |
 | DICT | Domain Dictionary (PO and IT terms) | docs/dictionary.md | 002 |
 

docs/sqa/reviews/rc-018-code-mil-006.md

@@ -0,0 +1,62 @@
+# SQA Review Record
+
+## Metadata
+| Key | Value |
+| --- | --- |
+| ID | RC-018 |
+| CrossReference | [MIL-006], [QC-PY-001] |
+
+## Version History
+| Date | Status | Author | Reviewer | Change | Commit |
+| --- | --- | --- | --- | --- | --- |
+| 2026-10-28 | Accepted | Jens Tirsvad Nielsen | AI as stand-in for S02 | Code review record | [afcb7d3] |
+
+---
+
+## Artifact Under Review
+
+- Instance reviewed: [MIL-006]
+- Checklist used: [QC-PY-001] (`QC-PY-001`)
+- Scope: full review of the source and tests added by MIL-006: BuyStrategy, buy-all plan, interval validation, --buy-all and --interval options, five attempt stale-read retry and 22 new tests (written with the python-developer agent); two batches of five 300 s container runs produced the comparison table and step-5.png
+- Language and domain: n/a
+- Language reviewer: none
+- Mode: autonomous, not independent (the reviewer is `AI as stand-in for S02`)
+
+## Checklist Results
+
+| # | Criterion | Status | Evidence/Notes |
+| --- | --- | --- | --- |
+| 1 | Packages, modules, functions, variables, classes and constants follow PEP 8 casing (`snake_case`, `PascalCase`, `UPPER_SNAKE`) | Pass | ruff (N rules) passes; names follow PEP 8 casing. |
+| 2 | Names state purpose in the domain's language; no unexplained abbreviations, no single-letter names outside tiny scopes | Pass | Names use the terms of DICT-001 (cookie, upgrade, bot); no single-letter names outside comprehensions. |
+| 3 | Code is produced by the project's formatter and passes its linter with no unexplained suppressions | Pass | `ruff format` and `ruff check` pass with the rules in `pyproject.toml`; no suppressions. |
+| 4 | Every function and method signature is type-annotated, including `-> None` | Pass | `mypy --strict` passes; every signature is annotated. |
+| 5 | No bare `except:`, no swallowed exceptions; specific exceptions are raised and the cause is kept (`raise ... from`) | Pass | No bare `except`; ruff B and S rules pass. |
+| 6 | No mutable default arguments and no shadowed builtins | Pass | No mutable defaults; ruff B006 and A rules pass. |
+| 7 | Files, locks and connections are managed with context managers | Pass | The browser is closed in a `finally` block in `main`. |
+| 8 | Public modules, classes and functions have docstrings that say what, not how | Pass | Public modules, classes and functions have Doxygen docstrings with `@brief`. |
+| 9 | Logging uses `logging`, not `print`; no secrets or personal data in log output | Pass | Diagnostics use `logging`; the required result line `cookies/second: N` is the program's output, not a log; no secrets are read or logged. |
+| 10 | Classes and operations trace to the Design Class Diagram they implement; deviations are recorded | N-A | No Design Class Diagram exists (ADR-0001 skips use case design); ADR-0002 records the layout instead. |
+| 11 | Tests exist for new behaviour, are named for the behaviour, and do not depend on order or the network | Pass | 116 tests pass with fakes; 100% coverage of the logic modules; a regression test covers the stale read found in a real run. |
+| 12 | Type checker runs in strict mode without errors; `Any` is justified in a comment | Pass | `mypy --strict` passes; no `Any`. |
+| 13 | Dependencies are declared and pinned in the project's dependency file, none unused | Pass | `pyproject.toml` lists Selenium as the only runtime dependency; dev extras are test and lint tools. |
+| 14 | Each piece of knowledge (a business rule, constant, format, validation or query) is defined in one place; code is merged only where it expresses the same knowledge, not where it merely looks alike | Pass | Constants live only in `constants.py`; rules are defined once. |
+| 15 | Imports point inward: business-rule modules import no framework, database, UI or delivery-mechanism code, and there are no import cycles | Pass | `domain` imports no Selenium; `application` depends on a port; no import cycles. |
+| 16 | SOLID holds: a class or module has one reason to change; new behaviour is added by extension, not by editing a type test in several places; subclasses honour the contract of their base; protocols are narrow; high-level code depends on protocols or abstract types and receives its implementations | Pass | Modules have one reason to change; the game is behind a narrow port. |
+| 17 | Source is laid out in the layers and folders of the clean architecture folder structure (`domain`, `application`, `infrastructure`, `presentation` packages under `src/`, and `unit`, `integration` and `e2e` under `tests/`), in `snake_case`, and imports between the layers point inward | Pass | Layers `domain`, `application`, `infrastructure` under `src/`, `unit` and `integration` under `tests/`; no `presentation` package by ADR-0002. |
+| 18 | File and folder names are English, contain no space and no character outside letters, digits, `-`, `_` and `.`, and follow the casing of the language for files | Pass | English names, snake_case files, no spaces. |
+
+## Overall Verdict
+
+Go — the code of MIL-006 meets every Mandatory criterion; `ruff`, `mypy --strict` and `pytest` were run and pass. The review is not independent: the AI wrote and reviewed it as stand-in for S02, and S01 can challenge it in the end-of-run summary.
+
+## Action Items
+
+| Action | Owner | Due |
+| --- | --- | --- |
+| None | S01 | - |
+
+---
+
+[MIL-006]: ../../milestones/mil-006-strategy.md
+[QC-PY-001]: ../../../framework/qc/code/qc-programming-python.md
+[afcb7d3]: https://git.tirsystem.com/Tirsvad-Udemy-100-days-of-code/048-the-coockie-factory-new/commit/afcb7d35a8d33f1eabacf6460769b887f326f6cc

docs/sqa/traceability-matrix.md

@@ -45,6 +45,7 @@ Tracks backward and forward links between artifact instances so that the Busines
 | Source and tests of [MIL-003] | Python source code | - | - | [MIL-003], [ADR-0002] | - | RC-015 |
 | Source and tests of [MIL-004] | Python source code | - | - | [MIL-004], [ADR-0002] | - | RC-016 |
 | Source and tests of [MIL-005] | Python source code | - | - | [MIL-005], [ADR-0002] | - | RC-017 |
+| Source and tests of [MIL-006] | Python source code | - | - | [MIL-006], [ADR-0002] | - | RC-018 |
 
 ## Concern Coverage
 

docs/wiki/Step-5-Improve-the-Strategy.md

@@ -0,0 +1,44 @@
+**English** · [Dansk](Step-5-Improve-the-Strategy-da) · [Bahasa Malaysia](Step-5-Improve-the-Strategy-ms)
+
+# Lecture step 5: tweak the algorithm
+
+![The game after the best run, checking every 10 seconds](https://git.tirsystem.com/Tirsvad-Udemy-100-days-of-code/048-the-coockie-factory-new/raw/branch/main/docs/images/step-5.png)
+
+## What the assignment asks
+
+Try another check interval (every second, every 10 seconds) or buy all affordable upgrades, and see whether the cookies per second go up.
+
+## What we built
+
+- `--interval SECONDS` sets the time between upgrade checks. It must be greater than 0; the default stays 5 seconds.
+- `--buy-all` buys every upgrade that still fits in the cookies you have, the most expensive first (`choose_affordable_upgrades`). Without it the bot buys one upgrade, the most expensive affordable one (`choose_most_expensive_affordable`).
+- Both rules are pure functions in the domain package, so they are unit tested without a browser. The strategy is a value (`BuyStrategy`), not a flag spread through the code.
+
+```bash
+cookie-clicker-bot --interval 10
+cookie-clicker-bot --interval 1 --buy-all
+```
+
+## What we measured
+
+Each row is a full 300 second run in a Docker container. Five containers ran at the same time on one computer, in two batches, so the numbers are good for comparing the rows with each other but a run alone is faster (our solo baseline of lecture step 4 was 18.9).
+
+| Check every | Strategy | Batch 1 | Batch 2 |
+| --- | --- | --- | --- |
+| 1 second | buy one | 13.5 | 13.5 |
+| 1 second | buy all | 13.5 | 13.5 |
+| 5 seconds (assignment) | buy one | 15.5 | 15.5 |
+| 5 seconds | buy all | crashed, see below | 14.5 |
+| 10 seconds | buy one | **18.2** | **18.2** |
+
+The best result is the 10 second interval with buy one. Why:
+
+- Checking more often is not better. Every check reads the page and takes time away from clicking, and the most expensive affordable product is usually only a little better than the cheaper one you could have bought a moment before.
+- Buy all makes no difference early in the game: only Cursor and Grandma are affordable, and the bot buys them anyway. It would matter later, when the cookie count holds several products at once.
+
+## What we gained in this step
+
+- **Small, pure rules are easy to compare.** Because the choice of upgrade does not touch Selenium, a new strategy is a new function plus a test.
+- **Measure, do not guess.** The result we expected (more checks, more cookies) was the opposite of what the runs showed.
+- **A second real bug.** The first batch crashed in one container: the game rewrites the counter every frame, and a computer under load made our single retry fail. The read now retries five times with a short pause. A test with a fake driver that goes stale four times shows it.
+- **Fair comparisons need the same conditions.** We ran the rows at the same time and report two batches, because one run can be lucky.

src/cookie_clicker_bot/application/game_loop.py

@@ -7,7 +7,12 @@ from collections.abc import Callable
 from dataclasses import dataclass
 
 from cookie_clicker_bot.application.ports import GamePort
-from cookie_clicker_bot.domain.upgrades import Upgrade, choose_most_expensive_affordable
+from cookie_clicker_bot.domain.buy_strategy import BuyStrategy
+from cookie_clicker_bot.domain.upgrades import (
+    Upgrade,
+    choose_affordable_upgrades,
+    choose_most_expensive_affordable,
+)
 
 
 @dataclass(frozen=True, slots=True)
@@ -43,11 +48,27 @@ def buy_most_expensive_upgrade(game: GamePort) -> Upgrade | None:
     return None
 
 
+def buy_upgrades(game: GamePort, strategy: BuyStrategy) -> list[Upgrade]:
+    """@brief Do one purchase round with the given strategy (lecture step 5).
+
+    @param game The game to play.
+    @param strategy BUY_ONE buys the most expensive affordable upgrade, BUY_ALL buys
+        every upgrade the cookies pay for.
+    @return The upgrades really bought, in order; a click that missed is left out.
+    """
+    if strategy is BuyStrategy.BUY_ONE:
+        bought = buy_most_expensive_upgrade(game)
+        return [] if bought is None else [bought]
+    plan = choose_affordable_upgrades(game.upgrades(), game.cookie_count())
+    return [upgrade for upgrade in plan if game.buy(upgrade)]
+
+
 def click_and_buy(
     game: GamePort,
     duration_seconds: float,
     check_interval_seconds: float,
     clock: Callable[[], float] = time.monotonic,
+    strategy: BuyStrategy = BuyStrategy.BUY_ONE,
 ) -> PlayResult:
     """@brief Click the cookie nonstop and check the upgrades at every interval.
 
@@ -56,6 +77,7 @@ def click_and_buy(
     @param check_interval_seconds Time between two upgrade checks; the first check
         comes one interval after the start.
     @param clock Monotonic clock in seconds; a test passes a fake one.
+    @param strategy What to buy at each check.
     @return The clicks, the names of the upgrades bought in order, and the time spent.
     """
     start = clock()
@@ -68,9 +90,7 @@ def click_and_buy(
         clicks += 1
         if now >= next_check:
             next_check = now + check_interval_seconds
-            bought = buy_most_expensive_upgrade(game)
-            if bought is not None:
-                purchases.append(bought.name)
+            purchases.extend(upgrade.name for upgrade in buy_upgrades(game, strategy))
     return PlayResult(
         clicks=clicks, purchases=tuple(purchases), elapsed_seconds=clock() - start
     )

src/cookie_clicker_bot/cli.py

@@ -11,6 +11,7 @@ from cookie_clicker_bot import constants
 from cookie_clicker_bot.application.game_loop import click_and_buy
 from cookie_clicker_bot.application.ports import GamePort
 from cookie_clicker_bot.application.report import format_result
+from cookie_clicker_bot.domain.buy_strategy import BuyStrategy
 from cookie_clicker_bot.infrastructure.browser import create_driver
 from cookie_clicker_bot.infrastructure.selenium_game import SeleniumGame
 
@@ -26,6 +27,23 @@ def create_game(headless: bool) -> GamePort:
     return SeleniumGame(create_driver(headless))
 
 
+def positive_float(text: str) -> float:
+    """@brief Read a number greater than zero from the command line.
+
+    @param text The argument text.
+    @return The number.
+    @throws argparse.ArgumentTypeError When the text is not a number above zero.
+    """
+    message = constants.POSITIVE_NUMBER_ERROR_TEMPLATE.format(value=text)
+    try:
+        value = float(text)
+    except ValueError:
+        raise argparse.ArgumentTypeError(message) from None
+    if not value > 0:
+        raise argparse.ArgumentTypeError(message)
+    return value
+
+
 def parse_args(argv: Sequence[str] | None = None) -> argparse.Namespace:
     """@brief Read the command line.
 
@@ -47,9 +65,17 @@ def parse_args(argv: Sequence[str] | None = None) -> argparse.Namespace:
     )
     parser.add_argument(
         "--interval",
-        type=float,
+        type=positive_float,
         default=constants.UPGRADE_CHECK_INTERVAL_SECONDS,
-        help="seconds between upgrade checks (default: %(default)s)",
+        help="seconds between upgrade checks, greater than 0 (default: %(default)s)",
+    )
+    parser.add_argument(
+        "--buy-all",
+        action="store_true",
+        help=(
+            "at each check buy every affordable upgrade, most expensive first "
+            "(default: buy only the most expensive affordable one)"
+        ),
     )
     parser.add_argument(
         "--headless",
@@ -87,7 +113,13 @@ def main(
         game.dismiss_language()
         if args.screenshot_start is not None:
             game.save_screenshot(args.screenshot_start)
-        result = click_and_buy(game, args.duration, args.interval)
+        strategy = BuyStrategy.BUY_ALL if args.buy_all else BuyStrategy.BUY_ONE
+        logger.info(
+            "checking upgrades every %s seconds, strategy %s",
+            args.interval,
+            strategy.value,
+        )
+        result = click_and_buy(game, args.duration, args.interval, strategy=strategy)
         for name in result.purchases:
             logger.info("bought %s", name)
         logger.info(

src/cookie_clicker_bot/constants.py

@@ -15,6 +15,9 @@ RUN_DURATION_SECONDS: Final[int] = 300
 ## Seconds between two checks for an affordable upgrade (lecture step 3).
 UPGRADE_CHECK_INTERVAL_SECONDS: Final[int] = 5
 
+## Error shown when a command-line number must be greater than zero.
+POSITIVE_NUMBER_ERROR_TEMPLATE: Final[str] = "{value!r} is not a number greater than 0"
+
 ## Longest time to wait for an element of the page, in seconds.
 WAIT_TIMEOUT_SECONDS: Final[int] = 20
 
@@ -72,6 +75,9 @@ MAGNITUDE_MULTIPLIERS: Final[dict[str, int]] = {
 ## Seconds between two polls while waiting for an element.
 POLL_INTERVAL_SECONDS: Final[float] = 0.2
 
+## Total attempts to read a value the game re-rendered under us (stale element).
+STALE_READ_ATTEMPTS: Final[int] = 5
+
 ## Environment variable that names the Chromium binary (set in the Docker image).
 CHROME_BIN_ENV: Final[str] = "CHROME_BIN"
 

src/cookie_clicker_bot/domain/buy_strategy.py

@@ -0,0 +1,14 @@
+"""@file buy_strategy.py
+@brief How many upgrades the bot buys at each check.
+"""
+
+from enum import Enum
+
+
+class BuyStrategy(Enum):
+    """@brief The purchase strategy of one upgrade check (lecture step 5)."""
+
+    ## Buy only the most expensive affordable upgrade (the assignment).
+    BUY_ONE = "buy-one"
+    ## Buy every upgrade the cookies pay for, most expensive first.
+    BUY_ALL = "buy-all"

src/cookie_clicker_bot/domain/upgrades.py

@@ -18,6 +18,27 @@ class Upgrade:
     price: int
 
 
+def choose_affordable_upgrades(
+    upgrades: Sequence[Upgrade], cookies: int
+) -> list[Upgrade]:
+    """@brief Plan a buy-all round: as many upgrades as the cookies pay for.
+
+    Walks the upgrades from most expensive to cheapest (the list order on a tie) and
+    takes each one whose price still fits in the cookies left.
+
+    @param upgrades The visible upgrades, in store order.
+    @param cookies The cookies the player has.
+    @return The upgrades to buy, most expensive first; empty when none is affordable.
+    """
+    plan: list[Upgrade] = []
+    remaining = cookies
+    for upgrade in sorted(upgrades, key=lambda candidate: -candidate.price):
+        if upgrade.price <= remaining:
+            plan.append(upgrade)
+            remaining -= upgrade.price
+    return plan
+
+
 def choose_most_expensive_affordable(
     upgrades: Sequence[Upgrade], cookies: int
 ) -> Upgrade | None:
@@ -27,7 +48,5 @@ def choose_most_expensive_affordable(
     @param cookies The cookies the player has.
     @return The chosen upgrade (the first on a tie), or None when none is affordable.
     """
-    affordable = [upgrade for upgrade in upgrades if upgrade.price <= cookies]
-    if not affordable:
-        return None
-    return max(affordable, key=lambda upgrade: upgrade.price)
+    plan = choose_affordable_upgrades(upgrades, cookies)
+    return plan[0] if plan else None

src/cookie_clicker_bot/infrastructure/selenium_game.py

@@ -151,13 +151,17 @@ class SeleniumGame:
         )
         return [self._read_upgrade(product) for product in products]
 
-    @staticmethod
-    def _read_again_if_stale(read: Callable[[], T]) -> T:
-        """@brief Run a read; repeat it once when the page re-rendered under it."""
-        try:
-            return read()
-        except StaleElementReferenceException:
-            return read()
+    def _read_again_if_stale(self, read: Callable[[], T]) -> T:
+        """@brief Run a read; repeat it while the page re-renders under it.
+
+        @throws StaleElementReferenceException When every attempt went stale.
+        """
+        for _ in range(constants.STALE_READ_ATTEMPTS - 1):
+            try:
+                return read()
+            except StaleElementReferenceException:
+                self._sleep(constants.POLL_INTERVAL_SECONDS)
+        return read()
 
     def buy(self, upgrade: Upgrade) -> bool:
         """@brief Buy an upgrade by clicking its product.

tests/integration/test_selenium_game.py

@@ -317,16 +317,49 @@ def test_upgrades_retries_once_when_a_product_goes_stale() -> None:
     assert make_game(driver).upgrades() == [Upgrade("product0", "Cursor", 15)]
 
 
+def test_cookies_per_second_succeeds_after_four_stale_attempts() -> None:
+    driver = FakeDriver()
+    attempts = _stale_for(4, FakeElement(text="per second: 3.5"))
+    driver.find_element = attempts.find_element  # type: ignore[method-assign]
+    fake_time = FakeTime()
+
+    assert make_game(driver, fake_time).cookies_per_second() == 3.5
+    assert attempts.calls == 5
+    assert fake_time.sleeps == [constants.POLL_INTERVAL_SECONDS] * 4
+
+
 def test_cookie_count_gives_up_when_the_counter_stays_stale() -> None:
     driver = FakeDriver()
-    driver.find_element = _always_stale  # type: ignore[method-assign]
+    attempts = _stale_for(100, FakeElement(text="42 cookies"))
+    driver.find_element = attempts.find_element  # type: ignore[method-assign]
+    fake_time = FakeTime()
 
     with pytest.raises(StaleElementReferenceException):
-        make_game(driver).cookie_count()
+        make_game(driver, fake_time).cookie_count()
+
+    assert attempts.calls == constants.STALE_READ_ATTEMPTS
+    assert fake_time.sleeps == [constants.POLL_INTERVAL_SECONDS] * (
+        constants.STALE_READ_ATTEMPTS - 1
+    )
 
 
-def _always_stale(by: str, value: str) -> FakeElement:
-    raise StaleElementReferenceException
+class _StaleFor:
+    """A `find_element` that goes stale for the first `stale` calls."""
+
+    def __init__(self, stale: int, element: FakeElement) -> None:
+        self._stale = stale
+        self._element = element
+        self.calls = 0
+
+    def find_element(self, by: str, value: str) -> FakeElement:
+        self.calls += 1
+        if self.calls <= self._stale:
+            raise StaleElementReferenceException
+        return self._element
+
+
+def _stale_for(stale: int, element: FakeElement) -> _StaleFor:
+    return _StaleFor(stale, element)
 
 
 def _stale_once_then(

tests/unit/test_cli.py

@@ -154,12 +154,12 @@ def test_main_logs_bought_only_for_real_purchases(
 ) -> None:
     caplog.set_level("INFO")
 
-    main(["--duration", "0.05", "--interval", "0"], lambda _h: RecordingGame())
+    main(["--duration", "0.05", "--interval", "0.001"], lambda _h: RecordingGame())
     assert "bought Cursor" in caplog.text
 
     caplog.clear()
     game = RecordingGame(buy_succeeds=False)
-    main(["--duration", "0.05", "--interval", "0"], lambda _h: game)
+    main(["--duration", "0.05", "--interval", "0.001"], lambda _h: game)
     assert "buy" in game.calls
     assert "bought Cursor" not in caplog.text
     assert "bought 0 upgrades" in caplog.text
@@ -172,3 +172,45 @@ def test_main_prints_nothing_on_stdout_when_the_run_fails(
         main(["--duration", "0"], lambda _headless: RecordingGame(fail_on_open=True))
 
     assert capsys.readouterr().out == ""
+
+
+def test_parse_args_buys_one_upgrade_unless_buy_all_is_given() -> None:
+    assert parse_args([]).buy_all is False
+    assert parse_args(["--buy-all"]).buy_all is True
+
+
+@pytest.mark.parametrize("value", ["0", "-1", "abc", "nan"])
+def test_parse_args_rejects_an_interval_that_is_not_positive(
+    value: str, capsys: pytest.CaptureFixture[str]
+) -> None:
+    with pytest.raises(SystemExit) as exit_info:
+        parse_args(["--interval", value])
+
+    assert exit_info.value.code == 2
+    assert "greater than 0" in capsys.readouterr().err
+
+
+def test_main_logs_the_interval_and_the_strategy(
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    caplog.set_level("INFO")
+
+    main(["--duration", "0"], lambda _h: RecordingGame())
+    assert "every 5 seconds, strategy buy-one" in caplog.text
+
+    caplog.clear()
+    main(
+        ["--duration", "0", "--interval", "2", "--buy-all"], lambda _h: RecordingGame()
+    )
+    assert "every 2.0 seconds, strategy buy-all" in caplog.text
+
+
+def test_main_buy_all_buys_every_affordable_upgrade_per_check(
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    caplog.set_level("INFO")
+    game = RecordingGame()
+
+    main(["--duration", "0.05", "--interval", "0.001", "--buy-all"], lambda _h: game)
+
+    assert "bought Cursor" in caplog.text

tests/unit/test_game_loop.py

@@ -7,9 +7,11 @@ from pathlib import Path
 from cookie_clicker_bot.application.game_loop import (
     PlayResult,
     buy_most_expensive_upgrade,
+    buy_upgrades,
     click_and_buy,
     click_cookie,
 )
+from cookie_clicker_bot.domain.buy_strategy import BuyStrategy
 from cookie_clicker_bot.domain.upgrades import Upgrade
 
 CURSOR = Upgrade("product0", "Cursor", 15)
@@ -169,3 +171,80 @@ def test_click_and_buy_stops_at_the_deadline_and_reports_elapsed_time() -> None:
 
     assert result.clicks == 300
     assert result.elapsed_seconds == 300.0
+
+
+def test_buy_upgrades_buy_one_buys_only_the_best_affordable() -> None:
+    game = FakeGame(cookies=120, upgrades=[CURSOR, GRANDMA])
+
+    assert buy_upgrades(game, BuyStrategy.BUY_ONE) == [GRANDMA]
+    assert game.bought == [GRANDMA]
+
+
+def test_buy_upgrades_buy_all_buys_every_affordable_upgrade() -> None:
+    game = FakeGame(cookies=120, upgrades=[CURSOR, GRANDMA])
+
+    assert buy_upgrades(game, BuyStrategy.BUY_ALL) == [GRANDMA, CURSOR]
+    assert game.bought == [GRANDMA, CURSOR]
+
+
+def test_buy_upgrades_buy_all_buys_nothing_when_too_poor() -> None:
+    game = FakeGame(cookies=10, upgrades=[CURSOR, GRANDMA])
+
+    assert buy_upgrades(game, BuyStrategy.BUY_ALL) == []
+    assert game.bought == []
+
+
+def test_buy_upgrades_buy_all_leaves_out_failed_buys() -> None:
+    game = FakeGame(cookies=120, upgrades=[CURSOR, GRANDMA], buy_succeeds=False)
+
+    assert buy_upgrades(game, BuyStrategy.BUY_ALL) == []
+    assert game.bought == [GRANDMA, CURSOR]
+
+
+def test_click_and_buy_defaults_to_buying_one_upgrade() -> None:
+    clock = FakeClock()
+    game = FakeGame(cookies=120, upgrades=[CURSOR, GRANDMA], clock=clock)
+
+    result = click_and_buy(game, 6, 5, clock)
+
+    assert result.purchases == ("Grandma",)
+
+
+def test_click_and_buy_buy_all_records_every_purchase_in_order() -> None:
+    clock = FakeClock()
+    game = FakeGame(cookies=120, upgrades=[CURSOR, GRANDMA], clock=clock)
+
+    result = click_and_buy(game, 6, 5, clock, BuyStrategy.BUY_ALL)
+
+    assert result.purchases == ("Grandma", "Cursor")
+
+
+def test_click_and_buy_buy_all_does_not_record_failed_buys() -> None:
+    clock = FakeClock()
+    game = FakeGame(
+        cookies=120, upgrades=[CURSOR, GRANDMA], clock=clock, buy_succeeds=False
+    )
+
+    result = click_and_buy(game, 6, 5, clock, BuyStrategy.BUY_ALL)
+
+    assert game.bought == [GRANDMA, CURSOR]
+    assert result.purchases == ()
+
+
+def test_click_and_buy_checks_every_second_with_a_one_second_interval() -> None:
+    clock = FakeClock()
+    game = FakeGame(cookies=105, upgrades=[GRANDMA], clock=clock)
+
+    click_and_buy(game, 4, 1, clock)
+
+    assert game.buy_times == [2.0, 3.0, 4.0]
+
+
+def test_click_and_buy_checks_every_ten_seconds_with_a_ten_second_interval() -> None:
+    clock = FakeClock()
+    game = FakeGame(cookies=105, upgrades=[GRANDMA], clock=clock)
+
+    result = click_and_buy(game, 25, 10, clock)
+
+    assert game.buy_times == [11.0, 21.0]
+    assert result.purchases == ("Grandma", "Grandma")

tests/unit/test_upgrades.py

@@ -2,7 +2,11 @@
 @brief Tests of the rule that picks the upgrade to buy.
 """
 
-from cookie_clicker_bot.domain.upgrades import Upgrade, choose_most_expensive_affordable
+from cookie_clicker_bot.domain.upgrades import (
+    Upgrade,
+    choose_affordable_upgrades,
+    choose_most_expensive_affordable,
+)
 
 CURSOR = Upgrade("product0", "Cursor", 15)
 GRANDMA = Upgrade("product1", "Grandma", 100)
@@ -33,3 +37,34 @@ def test_choose_takes_the_first_on_a_tie() -> None:
 
 def test_choose_ignores_the_order_of_the_list() -> None:
     assert choose_most_expensive_affordable([GRANDMA, CURSOR], 105) == GRANDMA
+
+
+def test_plan_skips_an_upgrade_the_remaining_cookies_cannot_pay() -> None:
+    assert choose_affordable_upgrades([CURSOR, GRANDMA, FARM], 105) == [GRANDMA]
+
+
+def test_plan_buys_several_upgrades_most_expensive_first() -> None:
+    assert choose_affordable_upgrades([CURSOR, GRANDMA, FARM], 120) == [GRANDMA, CURSOR]
+
+
+def test_plan_is_empty_when_nothing_is_affordable() -> None:
+    assert choose_affordable_upgrades([CURSOR, GRANDMA], 10) == []
+
+
+def test_plan_is_empty_without_upgrades() -> None:
+    assert choose_affordable_upgrades([], 1000) == []
+
+
+def test_plan_spends_the_whole_budget_on_equal_prices() -> None:
+    twin = Upgrade("product9", "Twin", 100)
+
+    assert choose_affordable_upgrades([GRANDMA, twin], 250) == [GRANDMA, twin]
+    assert choose_affordable_upgrades([twin, GRANDMA], 150) == [twin]
+
+
+def test_plan_does_not_change_the_given_list() -> None:
+    upgrades = [CURSOR, GRANDMA]
+
+    choose_affordable_upgrades(upgrades, 1000)
+
+    assert upgrades == [CURSOR, GRANDMA]