tests: resolve __file__ to be abs path

Author: waketzheng

tests/runtests.py

@@ -1,17 +1,18 @@
 import glob
 import os
 import subprocess
+from pathlib import Path
 
 # Change work dir if not in tests/
-tests_dir = os.path.dirname(__file__)
-if os.getcwd() != tests_dir:
+tests_dir = Path(__file__).parent.resolve()
+if Path.cwd() != tests_dir:
     os.chdir(tests_dir)
 
 tests = sorted(glob.glob("[A-Za-z]*.py"))
 excludes = ["runtests.py"]
 
-output_dir = os.path.join(os.path.dirname(__file__), "output")
-if not os.path.exists(output_dir):
+output_dir = tests_dir / "output"
+if not output_dir.exists():
     os.mkdir(output_dir)
 
 for test in tests: