I tried running the tests manually (./run-test262.sh). It fails:
File "src/test262.py", line 382, in validate
raise TypeError("Invalid value for negative phase: " + phase)
TypeError: Invalid value for negative phase: parse
Which refers to the line:
if phase not in [None, "early", "runtime"]:
raise TypeError("Invalid value for negative phase: " + phase)
The test harness has not been updated in two years. The tests themselves are under active development. It would be a good idea to pin the test and harness versions to something reasonable.