diff -r 000000000000 -r 6474c204b198 toolkit/components/telemetry/tests/unit/test_TelemetryLog.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetryLog.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,45 @@
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const Cu = Components.utils;
+
+Cu.import("resource://gre/modules/TelemetryLog.jsm", this);
+Cu.import("resource://gre/modules/TelemetryPing.jsm", this);
+
+const TEST_PREFIX = "TEST-";
+const TEST_REGEX = new RegExp("^" + TEST_PREFIX);
+
+function check_event(event, id, data)
+{
+  do_print("Checking message " + id);
+  do_check_eq(event[0], id);
+  do_check_true(event[1] > 0);
+
+  if (data === undefined) {
+    do_check_true(event.length == 2);
+  } else {
+    do_check_eq(event.length, data.length + 2);
+    for (var i = 0; i < data.length; ++i) {
+      do_check_eq(typeof(event[i + 2]), "string");
+      do_check_eq(event[i + 2], data[i]);
+    }
+  }
+}
+
+function run_test()
+{
+  TelemetryLog.log(TEST_PREFIX + "1", ["val", 123, undefined]);
+  TelemetryLog.log(TEST_PREFIX + "2", []);
+  TelemetryLog.log(TEST_PREFIX + "3");
+
+  var log = TelemetryPing.getPayload().log.filter(function(e) {
+    // Only want events that were generated by the test.
+    return TEST_REGEX.test(e[0]);
+  });
+
+  do_check_eq(log.length, 3);
+  check_event(log[0], TEST_PREFIX + "1", ["val", "123", "undefined"]);
+  check_event(log[1], TEST_PREFIX + "2", []);
+  check_event(log[2], TEST_PREFIX + "3", undefined);
+  do_check_true(log[0][1] <= log[1][1]);
+  do_check_true(log[1][1] <= log[2][1]);
+}