gh-153953: Increase test coverage for the wave module

[fedonman]

Adds tests for previously-uncovered code paths in Lib/wave.py, all reachable through the public API and deterministic across platforms.

Wave_write parameter validation

• setnchannels() rejecting a non-positive channel count
• getnchannels() / getsampwidth() / getframerate() / getparams() raising when parameters are unset
• setsampwidth() rejecting out-of-range widths
• setcomptype() / setformat() rejecting unsupported values
• the "cannot change parameters after starting to write" guard on every setter (setnchannels, setsampwidth, setframerate, setnframes, setcomptype, setformat, setparams)
• tell()

Wave_read error handling

• rejecting a WAVE_FORMAT_EXTENSIBLE file whose SubFormat GUID is not PCM
• raising EOFError on a truncated fmt chunk (missing header / missing sample width)
• skipping an unknown, odd-sized chunk between fmt and data
• getfp()
• closing the underlying file when opening a malformed file by path fails

wave.open()

• rejecting an invalid mode

Measured with the stdlib trace module while running test_wave, line coverage of Lib/wave.py rises from 317/449 to 345/449 executable lines.

This is a test-only change with no behavior change, so no Misc/NEWS.d entry is included. ./python -m test -R 3:3 test_wave reports no reference leaks.

Fixes #153953.

• Issue: Increase test coverage for the wave module #153953

[fedonman]

@vstinner comments addressed, you may review again.

[vstinner]

I would prefer to not ignore error on close(). I suggest setting all parameters so close() doesn't fail. Nitpick: I also prefer declaring the close function before it's being used by open_writer():

Suggested change

	def open_writer(self):
	w = wave.open(io.BytesIO(), 'wb')
	self.addCleanup(self._close_quietly, w)
	return w
	@staticmethod
	def _close_quietly(w):
	# A writer whose required parameters are never set raises on close;
	# swallow that so it does not mask the behaviour under test.
	try:
	w.close()
	except wave.Error:
	pass
	@staticmethod
	def _close(w):
	try:
	# Make sure that all parameters are set
	w.setnchannels(1)
	w.setsampwidth(2)
	w.setframerate(44100)
	except wave.Error:
	# Ignore "cannot change parameters after starting to write" error
	pass
	w.close()
	def open_writer(self):
	w = wave.open(io.BytesIO(), 'wb')
	self.addCleanup(self._close, w)
	return w

[vstinner]

I suggest testing getnframes() at the same time, use a shorter test name, and write twice (just in case):

Suggested change

	def test_tell_reports_frames_written(self):
	w = self.open_writer()
	w.setnchannels(1)
	w.setsampwidth(2)
	w.setframerate(44100)
	self.assertEqual(w.tell(), 0)
	w.writeframes(b'\x00\x00' * 5)
	self.assertEqual(w.tell(), 5)
	def test_tell(self):
	def check_nframes(nframes):
	self.assertEqual(w.tell(), nframes)
	self.assertEqual(w.getnframes(), nframes)
	w = self.open_writer()
	w.setnchannels(1)
	w.setsampwidth(2)
	w.setframerate(44100)
	check_nframes(0)
	frame = b'\x00\x00'
	w.writeframes(frame * 5)
	check_nframes(5)
	w.writeframes(frame * 3)
	check_nframes(8)

[vstinner]

We can reuse the same writer object for all tests, no need to create a fresh writer at each iteration:

Suggested change

	def test_cannot_change_params_after_write(self):
	setters = (
	('setnchannels', (1,)),
	('setsampwidth', (2,)),
	('setframerate', (44100,)),
	('setnframes', (10,)),
	('setcomptype', ('NONE', 'not compressed')),
	('setformat', (wave.WAVE_FORMAT_PCM,)),
	('setparams', ((1, 2, 44100, 0, 'NONE', 'not compressed'),)),
	)
	for name, args in setters:
	with self.subTest(setter=name):
	w = self.open_writer()
	w.setnchannels(1)
	w.setsampwidth(2)
	w.setframerate(44100)
	w.writeframes(b'\x00\x00')
	with self.assertRaisesRegex(wave.Error,
	'cannot change parameters'):
	getattr(w, name)(*args)
	def test_cannot_change_params_after_write(self):
	w = self.open_writer()
	w.setnchannels(1)
	w.setsampwidth(2)
	w.setframerate(44100)
	w.writeframes(b'\x00\x00')
	setters = (
	('setnchannels', (1,)),
	('setsampwidth', (2,)),
	('setframerate', (44100,)),
	('setnframes', (10,)),
	('setcomptype', ('NONE', 'not compressed')),
	('setformat', (wave.WAVE_FORMAT_PCM,)),
	('setparams', ((1, 2, 44100, 0, 'NONE', 'not compressed'),)),
	)
	for name, args in setters:
	with self.subTest(setter=name):
	with self.assertRaisesRegex(wave.Error,
	'cannot change parameters'):
	getattr(w, name)(*args)