[test] Make get_tests return only files

[aheejin]

Currently get_tests returns files and directories, especially when the extension is not given. This makes get_tests return a directory like test/wasm2js/ as a test.

wasm2js.py's check_for_stale_files errors out when there are files within test/wasm2js/ whose basenames don't match any files within any of test/, test/spec/, test/wasm2js/.

binaryen/scripts/test/wasm2js.py

Lines 33 to 46 in 1d615b3

	def check_for_stale_files():
	if shared.options.test_name_filter:
	return
	# TODO(sbc): Generalize and apply other test suites
	all_tests = []
	for t in tests + spec_tests + wasm2js_tests:
	all_tests.append(os.path.basename(os.path.splitext(t)[0]))
	all_files = os.listdir(shared.get_test_dir('wasm2js'))
	for f in all_files:
	prefix = f.split('.')[0]
	if prefix not in all_tests:
	shared.fail_with_error('orphan test output: %s' % f)

wasm2js.wast.asserts is apparently a special case for asserts test:

binaryen/scripts/test/wasm2js.py

Line 28 in 1d615b3

assert_tests = ['wasm2js.wast.asserts']

and this doesn't seem to have the matching wast tests in the three test directories. But it just happened to not error out because get_tests returns directory names too and one of them was wasm2js (test/wasm2js/ directory).

This makes get_tests return only files, and make files in assert_tests not error out additionally.