--- a/testing/mozbase/docs/mozlog_structured.rst
+++ b/testing/mozbase/docs/mozlog_structured.rst
@@ -79,16 +79,20 @@ emitted:
   Emitted when the testsuite is finished and no more results will be produced.
 
 ``test_start``
   Emitted when a test is being started.
 
   ``test``
     A unique id for the test (string or list of strings).
 
+  ``path``
+    Optional path to the test relative to some base (typically the root of the
+    source tree. Mainly used when ``test`` id is not a path (string).
+
 ``test_status``
   Emitted for a test which has subtests to record the result of a
   single subtest.
 
   ``test``
     The same unique id for the test as in the ``test_start`` message.
 
   ``subtest``

--- a/testing/mozbase/mozlog/mozlog/structured/structuredlog.py
+++ b/testing/mozbase/mozlog/mozlog/structured/structuredlog.py
@@ -19,16 +19,17 @@ from logtypes import log_action, convert
 Allowed actions, and subfields:
   suite_start
       tests  - List of test names
 
   suite_end
 
   test_start
       test - ID for the test
+      path - Relative path to test (optional)
 
   test_end
       test - ID for the test
       status [PASS | FAIL | OK | ERROR |
               TIMEOUT | CRASH | ASSERT | SKIP] - test status
       expected [As for status] - Status that the test was expected to get,
                                  or absent if the test got the expected status
       extra - Dictionary of harness-specific extra information e.g. debug info
@@ -243,21 +244,24 @@ class StructuredLogger(object):
         if not self._state.suite_started:
             self.error("Got suite_end message before suite_start.")
             return
 
         self._state.suite_started = False
 
         self._log_data("suite_end")
 
-    @log_action(TestId("test"))
+    @log_action(TestId("test"),
+                Unicode("path", default=None, optional=True))
     def test_start(self, data):
         """Log a test_start message
 
         :param test: Identifier of the test that will run.
+        :param path: Path to test relative to some base (typically the root of
+                     the source tree).
         """
         if not self._state.suite_started:
             self.error("Got test_start message before suite_start for test %s" %
                        data["test"])
             return
         if data["test"] in self._state.running_tests:
             self.error("test_start for %s logged while in progress." %
                        data["test"])

--- a/testing/mozbase/mozlog/tests/test_structured.py
+++ b/testing/mozbase/mozlog/tests/test_structured.py
@@ -112,19 +112,20 @@ class TestStructuredLog(BaseStructuredTe
         self.assert_log_equals({"action": "suite_end"})
 
     def test_start(self):
         self.logger.suite_start([])
         self.logger.test_start("test1")
         self.assert_log_equals({"action": "test_start",
                                 "test":"test1"})
 
-        self.logger.test_start(("test1", "==", "test1-ref"))
+        self.logger.test_start(("test1", "==", "test1-ref"), path="path/to/test")
         self.assert_log_equals({"action": "test_start",
-                                "test":("test1", "==", "test1-ref")})
+                                "test":("test1", "==", "test1-ref"),
+                                "path": "path/to/test"})
         self.logger.suite_end()
 
     def test_start_inprogress(self):
         self.logger.suite_start([])
         self.logger.test_start("test1")
         self.logger.test_start("test1")
         self.assert_log_equals({"action": "log",
                                 "message": "test_start for test1 logged while in progress.",