Fix running just a single spec test via check.py spec --spec-test foo. NFC (#6580)

Author: sbc100

scripts/test/shared.py

@@ -79,7 +79,7 @@ def parse_args(args):
         help=('If specified, all unfreed (but still referenced) pointers at the'
               ' end of execution are considered memory leaks. Default: disabled.'))
     parser.add_argument(
-        '--spec-test', action='append', nargs='*', default=[], dest='spec_tests',
+        '--spec-test', action='append', default=[], dest='spec_tests',
         help='Names specific spec tests to run.')
     parser.add_argument(
         'positional_args', metavar='TEST_SUITE', nargs='*',
@@ -159,7 +159,6 @@ def warn(text):
 
 if not os.path.exists(options.out_dir):
     os.makedirs(options.out_dir)
-os.chdir(options.out_dir)
 
 
 # Finds the given executable 'program' in PATH.
@@ -384,10 +383,12 @@ def get_tests(test_dir, extensions=[], recursive=False):
     return sorted(tests)
 
 
-if not options.spec_tests:
-    options.spec_tests = get_tests(get_test_dir('spec'), ['.wast'])
+if options.spec_tests:
+    options.spec_tests = [os.path.abspath(t) for t in options.spec_tests]
 else:
-    options.spec_tests = options.spec_tests[:]
+    options.spec_tests = get_tests(get_test_dir('spec'), ['.wast'])
+
+os.chdir(options.out_dir)
 
 # 11/27/2019: We updated the spec test suite to upstream spec repo. For some
 # files that started failing after this update, we added the new files to this