Bug 1626734 - Add some gtests for SystemTimeConverter. r=karlt

Differential Revision: https://phabricator.services.mozilla.com/D73740

widget/SystemTimeConverter.h

@@ -25,7 +25,7 @@ namespace mozilla {
 // For performance reasons, this class is careful to minimize calls to the
 // native "current time" function (e.g. gdk_x11_server_get_time) since this can
 // be slow.
-template <typename Time>
+template <typename Time, typename TimeStampNowProvider = TimeStamp>
 class SystemTimeConverter {
  public:
   SystemTimeConverter()
@@ -42,7 +42,7 @@ class SystemTimeConverter {
   template <typename CurrentTimeGetter>
   mozilla::TimeStamp GetTimeStampFromSystemTime(
       Time aTime, CurrentTimeGetter& aCurrentTimeGetter) {
-    TimeStamp roughlyNow = TimeStamp::Now();
+    TimeStamp roughlyNow = TimeStampNowProvider::Now();
 
     // If the reference time is not set, use the current time value to fill
     // it in.
@@ -176,7 +176,7 @@ class SystemTimeConverter {
   void UpdateReferenceTime(Time aReferenceTime,
                            const CurrentTimeGetter& aCurrentTimeGetter) {
     Time currentTime = aCurrentTimeGetter.GetCurrentTime();
-    TimeStamp currentTimeStamp = TimeStamp::Now();
+    TimeStamp currentTimeStamp = TimeStampNowProvider::Now();
     Time timeSinceReference = currentTime - aReferenceTime;
     TimeStamp referenceTimeStamp =
         currentTimeStamp - TimeDuration::FromMilliseconds(timeSinceReference);

widget/moz.build

@@ -73,7 +73,10 @@ elif toolkit == 'cocoa':
         'nsINativeMenuService.h',
     ]
 
-TEST_DIRS += ['tests']
+TEST_DIRS += [
+    'tests',
+    'tests/gtest'
+]
 
 DIRS += ['headless']
 

widget/tests/gtest/TestTimeConverter.cpp

@@ -0,0 +1,126 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "gtest/gtest.h"
+#include "mozilla/TimeStamp.h"
+#include "SystemTimeConverter.h"
+
+using mozilla::SystemTimeConverter;
+using mozilla::TimeDuration;
+using mozilla::TimeStamp;
+
+namespace {
+
+// This class provides a mock implementation of the CurrentTimeGetter template
+// type used in SystemTimeConverter. It can be constructed with a particular
+// Time and always returns that Time.
+template <typename Time>
+class MockCurrentTimeGetter {
+ public:
+  MockCurrentTimeGetter() : mTime(0) {}
+  explicit MockCurrentTimeGetter(Time aTime) : mTime(aTime) {}
+
+  // Methods needed for CurrentTimeGetter compatibility
+  Time GetCurrentTime() const { return mTime; }
+  void GetTimeAsyncForPossibleBackwardsSkew(const TimeStamp& aNow) {}
+
+ private:
+  Time mTime;
+};
+
+// This is another mock implementation of the CurrentTimeGetter template
+// type used in SystemTimeConverter, except this asserts that it will not be
+// used. i.e. it should only be used in calls to SystemTimeConverter that we
+// know will not invoke it.
+template <typename Time>
+class UnusedCurrentTimeGetter {
+ public:
+  Time GetCurrentTime() const {
+    EXPECT_TRUE(false);
+    return 0;
+  }
+
+  void GetTimeAsyncForPossibleBackwardsSkew(const TimeStamp& aNow) {
+    EXPECT_TRUE(false);
+  }
+};
+
+// This class provides a mock implementation of the TimeStampNowProvider
+// template type used in SystemTimeConverter. It also has other things in it
+// that allow the test to better control time for testing purposes.
+class MockTimeStamp {
+ public:
+  // This should generally be called at the start of every test function, as
+  // it will initialize this class's static fields to sane values. In particular
+  // it will initialize the baseline TimeStamp against which all other
+  // TimeStamps are compared.
+  static void Init() {
+    sBaseline = TimeStamp::Now();
+    sTimeStamp = sBaseline;
+  }
+
+  // Advance the timestamp returned by `MockTimeStamp::Now()`
+  static void Advance(double ms) {
+    sTimeStamp += TimeDuration::FromMilliseconds(ms);
+  }
+
+  // Returns the baseline TimeStamp, that is used as a fixed reference point
+  // in time against which other TimeStamps can be compared. This is needed
+  // because mozilla::TimeStamp itself doesn't provide any conversion to
+  // human-readable strings, and we need to convert it to a TimeDuration in
+  // order to get that. This baseline TimeStamp can be used to turn an
+  // arbitrary TimeStamp into a TimeDuration.
+  static TimeStamp Baseline() { return sBaseline; }
+
+  // This is the method needed for TimeStampNowProvider compatibility, and
+  // simulates `TimeStamp::Now()`
+  static TimeStamp Now() { return sTimeStamp; }
+
+ private:
+  static TimeStamp sTimeStamp;
+  static TimeStamp sBaseline;
+};
+
+TimeStamp MockTimeStamp::sTimeStamp;
+TimeStamp MockTimeStamp::sBaseline;
+
+// Could have platform-specific implementations of this using DWORD, guint32,
+// etc behind ifdefs. But this is sufficient for now.
+using GTestTime = uint32_t;
+using TimeConverter = SystemTimeConverter<GTestTime, MockTimeStamp>;
+
+}  // namespace
+
+// Checks the expectation that the TimeStamp `ts` is exactly `ms` milliseconds
+// after the baseline timestamp. This is a macro so gtest still gives us useful
+// line numbers for failures.
+#define EXPECT_TS(ts, ms) \
+  EXPECT_EQ((ts)-MockTimeStamp::Baseline(), TimeDuration::FromMilliseconds(ms))
+
+TEST(TimeConverter, SanityCheck)
+{
+  MockTimeStamp::Init();
+
+  MockCurrentTimeGetter timeGetter(10);
+  UnusedCurrentTimeGetter<GTestTime> unused;
+  TimeConverter converter;
+
+  // This call sets the reference time and timestamp
+  TimeStamp ts = converter.GetTimeStampFromSystemTime(10, timeGetter);
+  EXPECT_TS(ts, 0);
+
+  // Advance "TimeStamp::Now" by 10ms, use the same event time and OS time.
+  // Since the event time is the same as before, we expect to get back the
+  // same TimeStamp as before too, despite Now() changing.
+  MockTimeStamp::Advance(10);
+  ts = converter.GetTimeStampFromSystemTime(10, unused);
+  EXPECT_TS(ts, 0);
+
+  // Now let's use an event time 20ms after the old event. This will trigger
+  // forward skew detection and resync the TimeStamp for the new event to Now().
+  ts = converter.GetTimeStampFromSystemTime(30, unused);
+  EXPECT_TS(ts, 10);
+}

widget/tests/gtest/moz.build

@@ -0,0 +1,15 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+UNIFIED_SOURCES = [
+    'TestTimeConverter.cpp',
+]
+
+FINAL_LIBRARY = 'xul-gtest'
+
+LOCAL_INCLUDES += [
+    '/widget',
+]