Add a trivial gmtime(3) test.

Change-Id: I849f200a455cd6971646fa45766ab22ba19fb866
diff --git a/tests/time_test.cpp b/tests/time_test.cpp
index 9a5a706..0ad4763 100644
--- a/tests/time_test.cpp
+++ b/tests/time_test.cpp
@@ -42,3 +42,15 @@
   ASSERT_EQ(2678400, mktime_tz(&epoch, "PST"));
 }
 #endif
+
+TEST(time, gmtime) {
+  time_t t = 0;
+  tm* broken_down = gmtime(&t);
+  ASSERT_TRUE(broken_down != NULL);
+  ASSERT_EQ(0, broken_down->tm_sec);
+  ASSERT_EQ(0, broken_down->tm_min);
+  ASSERT_EQ(0, broken_down->tm_hour);
+  ASSERT_EQ(1, broken_down->tm_mday);
+  ASSERT_EQ(0, broken_down->tm_mon);
+  ASSERT_EQ(1970, broken_down->tm_year + 1900);
+}