Day 12: 測試與可重複的程式

參考實作（兩個檔案放在同一目錄；已用 Python 3.13 和 3.14 驗證）：
# file: counter.py
def count_non_empty(lines):
"""Return how many items contain non-whitespace text.

Raise TypeError if an item is not a str.
"""
count = 0
for line in lines:
if not isinstance(line, str):
raise TypeError(f"expected str, got {type(line).__name__}")
if line.strip():
count += 1
return count
# end file
# file: test_counter.py
import unittest

from counter import count_non_empty

class CounterTests(unittest.TestCase):
def test_empty_list_returns_zero(self):
self.assertEqual(count_non_empty([]), 0)

def test_whitespace_only_line_is_ignored(self):
self.assertEqual(count_non_empty([" \t\n"]), 0)

def test_mixed_lines_count_only_non_empty(self):
self.assertEqual(count_non_empty(["alpha\n", " \n", "", "beta"]), 2)

def test_non_string_item_raises_type_error(self):
with self.assertRaises(TypeError):
count_non_empty(["alpha", None])

if __name__ == "__main__":
unittest.main()
# end file
在該目錄以發現方式執行：
$ python -m unittest -v
test_empty_list_returns_zero (test_counter.CounterTests.test_empty_list_returns_zero) ... ok
test_mixed_lines_count_only_non_empty (test_counter.CounterTests.test_mixed_lines_count_only_non_empty) ... ok
test_non_string_item_raises_type_error (test_counter.CounterTests.test_non_string_item_raises_type_error) ... ok
test_whitespace_only_line_is_ignored (test_counter.CounterTests.test_whitespace_only_line_is_ignored) ... ok

----------------------------------------------------------------------
Ran 4 tests in 0.001s

OK
直接執行檔案時，只會透過 unittest.main() 執行這個檔案裡的測試，模組顯示為 __main__：
$ python test_counter.py -v
test_empty_list_returns_zero (__main__.CounterTests.test_empty_list_returns_zero) ... ok
test_mixed_lines_count_only_non_empty (__main__.CounterTests.test_mixed_lines_count_only_non_empty) ... ok
test_non_string_item_raises_type_error (__main__.CounterTests.test_non_string_item_raises_type_error) ... ok
test_whitespace_only_line_is_ignored (__main__.CounterTests.test_whitespace_only_line_is_ignored) ... ok

----------------------------------------------------------------------
Ran 4 tests in 0.001s

OK
OK 證明了什麼：在這個直譯器上，這四個輸入的每條斷言都成立，包括 None 拋出了 TypeError。沒證明什麼：count_non_empty 對沒人測過的輸入（例如其他非 str 型別或少見的空白字元）也正確。

參考實作：
# file: scores.py
def summarize_scores(path):
"""Return {name: highest score} for rows like "ana,7".

Strict contract: a missing file raises FileNotFoundError and a
malformed score raises ValueError; blank lines are ignored.
"""
best = {}
with open(path, encoding="utf-8") as f:
for lineno, line in enumerate(f, 1):
line = line.strip()
if not line:
continue
name, _, raw = line.rpartition(",")
try:
score = int(raw)
except ValueError:
raise ValueError(f"line {lineno}: invalid score {raw!r}") from None
if name not in best or score > best[name]:
best[name] = score
return best
# end file
把上面的 test_scores.py 放在同一目錄：
$ python -m unittest -v
test_invalid_score (test_scores.SummarizeTests.test_invalid_score) ... ok
test_missing_file (test_scores.SummarizeTests.test_missing_file) ... ok
test_valid_file (test_scores.SummarizeTests.test_valid_file) ... ok

----------------------------------------------------------------------
Ran 3 tests in 0.002s

OK
在同一目錄做誘餌檢查（bash）：
$ echo "ana,1" > does-not-exist.txt
$ python -m unittest -v
test_invalid_score (test_scores.SummarizeTests.test_invalid_score) ... ok
test_missing_file (test_scores.SummarizeTests.test_missing_file) ... ok
test_valid_file (test_scores.SummarizeTests.test_valid_file) ... ok

----------------------------------------------------------------------
Ran 3 tests in 0.002s

OK
同樣三個測試通過：工作目錄裡的檔案既不能滿足也不能破壞 test_missing_file。每個預期值都在斷言中可見：{"ana": 8, "bo": 9}（ana 的 8 勝過 7）、FileNotFoundError，以及 bo,x9 這一行對應的 ValueError。

修復前的觀察（節錄；traceback 的行因環境而異）：
$ python -m unittest -v
test_three_rows (test_total.TotalTests.test_three_rows) ... FAIL

======================================================================
FAIL: test_three_rows (test_total.TotalTests.test_three_rows)
----------------------------------------------------------------------
Traceback (most recent call last):
...
AssertionError: 20 != 30

----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (failures=1)
診斷。症狀：總分是 20 而不是 30——恰好少了一行 10 分。證據：fixture 在測試內寫入，因此不涉及外部檔案、工作目錄或已安裝的套件，而且你執行的每個直譯器下失敗都相同。假設：readlines()[1:] 把第 1 行當作表頭丟棄，但 fixture 的第一行是 a,10。分類：程式缺陷；文件規定的格式沒有表頭行，所以測試的 30 是對的。最小修復——只改 total.py 的一行，test_total.py 不變：
# file: total.py
def total_score(path):
"""Return the sum of the scores in rows like "a,10" (no header row)."""
total = 0
with open(path, encoding="utf-8") as f:
lines = f.readlines()
for line in lines:
name, _, raw = line.strip().rpartition(",")
total += int(raw)
return total
# end file
重跑：
$ python -m unittest -v
test_three_rows (test_total.TotalTests.test_three_rows) ... ok

----------------------------------------------------------------------
Ran 1 test in 0.001s

OK

參考答案——先記錄你獨立完成的嘗試，再來對照。
# file: scores.py
import sys

def summarize_scores(path):
"""Return {name: highest score} for rows like "ana,7".

Strict contract: a missing file raises FileNotFoundError and a
malformed score raises ValueError; blank lines are ignored.
"""
best = {}
with open(path, encoding="utf-8") as f:
for lineno, line in enumerate(f, 1):
line = line.strip()
if not line:
continue
name, _, raw = line.rpartition(",")
try:
score = int(raw)
except ValueError:
raise ValueError(f"line {lineno}: invalid score {raw!r}") from None
if name not in best or score > best[name]:
best[name] = score
return best

def main(argv=None):
args = sys.argv[1:] if argv is None else argv
if len(args) != 1:
print("usage: python scores.py SCORES_FILE", file=sys.stderr)
return 2
try:
result = summarize_scores(args[0])
except FileNotFoundError as e:
print(f"error: file not found: {e.filename}", file=sys.stderr)
return 1
except ValueError as e:
print(f"error: {e}", file=sys.stderr)
return 1
print(result)
return 0

if __name__ == "__main__":
sys.exit(main())
# end file
# file: test_scores.py
import tempfile
import unittest
from pathlib import Path

from scores import summarize_scores

class SummarizeTests(unittest.TestCase):
def test_valid_file(self):
with tempfile.TemporaryDirectory() as d:
p = Path(d) / "scores.txt"
p.write_text("ana,7\nbo,9\nana,8\n", encoding="utf-8")
self.assertEqual(summarize_scores(str(p)), {"ana": 8, "bo": 9})

def test_missing_file(self):
with tempfile.TemporaryDirectory() as d:
missing = Path(d) / "does-not-exist.txt"
with self.assertRaises(FileNotFoundError):
summarize_scores(str(missing))

def test_invalid_score(self):
with tempfile.TemporaryDirectory() as d:
p = Path(d) / "scores.txt"
p.write_text("ana,7\nbo,x9\n", encoding="utf-8")
with self.assertRaises(ValueError):
summarize_scores(str(p))
# end file
# file: requirements.txt
# stdlib only, no third-party dependencies
# end file
在只含這三個檔案的目錄中執行：
$ python -m unittest -v
test_invalid_score (test_scores.SummarizeTests.test_invalid_score) ... ok
test_missing_file (test_scores.SummarizeTests.test_missing_file) ... ok
test_valid_file (test_scores.SummarizeTests.test_valid_file) ... ok

----------------------------------------------------------------------
Ran 3 tests in 0.002s

OK
然後是命令列（bash；額外的 fixture 檔案在測試執行之後才建立）：
$ printf 'ana,7\nbo,9\nana,8\n' > s1.txt
$ python scores.py s1.txt; echo "exit $?"
{'ana': 8, 'bo': 9}
exit 0
$ python scores.py nope.txt; echo "exit $?"
error: file not found: nope.txt
exit 1
$ printf 'ana,7\nbo,x9\n' > s2.txt
$ python scores.py s2.txt; echo "exit $?"
error: line 2: invalid score 'x9'
exit 1
用 python -c "import sys; print(sys.executable, sys.version)" 記錄直譯器。恢復計畫：Ran 0 tests → 檢查 test_*.py 命名和發現目錄（day-12-act-01）；ModuleNotFoundError → 檢查直譯器和工作目錄（day-11）；FileNotFoundError → 檢查路徑（day-10）；斷言失敗 → 先診斷再改（day-12-act-03）。