Bug 1531234 - Write JS test structured logs to main_raw.log instead of intermixing them in stdout r=ahal

Differential Revision: https://phabricator.services.mozilla.com/D21483

--HG--
extra : moz-landing-system : lando

js/src/tests/lib/structuredlog.py

@@ -1,6 +1,8 @@
 # produce mozlog-compatible log messages, following the spec at
 # https://mozbase.readthedocs.io/en/latest/mozlog.html
 
+from __future__ import print_function
+
 import json
 import os
 
@@ -14,6 +16,8 @@ class TestLogger(object):
             'thread': threadname,
             'pid': os.getpid(),
         }
+        directory = os.environ.get("MOZ_UPLOAD_DIR", ".")
+        self.fh = open(os.path.join(directory, threadname + "_raw.log"), "a")
 
     def _record(self, **kwargs):
         record = self.template.copy()
@@ -23,7 +27,7 @@ class TestLogger(object):
         return record
 
     def _log_obj(self, obj):
-        print(json.dumps(obj, sort_keys=True))
+        print(json.dumps(obj, sort_keys=True), file=self.fh)
 
     def _log(self, **kwargs):
         self._log_obj(self._record(**kwargs))