Basic unit tests for update_current_time().

This function is about to get more complicated, so we should track
how it's working.

src/test/include.am

@@ -139,6 +139,7 @@ src_test_test_SOURCES = \
 	src/test/test_keypin.c \
 	src/test/test_link_handshake.c \
 	src/test/test_logging.c \
+	src/test/test_mainloop.c \
 	src/test/test_microdesc.c \
 	src/test/test_nodelist.c \
 	src/test/test_oom.c \

src/test/test.c

@@ -859,6 +859,7 @@ struct testgroup_t testgroups[] = {
   { "introduce/", introduce_tests },
   { "keypin/", keypin_tests },
   { "link-handshake/", link_handshake_tests },
+  { "mainloop/", mainloop_tests },
   { "nodelist/", nodelist_tests },
   { "oom/", oom_tests },
   { "oos/", oos_tests },

src/test/test.h

@@ -234,6 +234,7 @@ extern struct testcase_t introduce_tests[];
 extern struct testcase_t keypin_tests[];
 extern struct testcase_t link_handshake_tests[];
 extern struct testcase_t logging_tests[];
+extern struct testcase_t mainloop_tests[];
 extern struct testcase_t microdesc_tests[];
 extern struct testcase_t nodelist_tests[];
 extern struct testcase_t oom_tests[];

src/test/test_mainloop.c

@@ -0,0 +1,102 @@
+/* Copyright (c) 2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file test_mainloop.c
+ * \brief Tests for functions closely related to the Tor main loop
+ */
+
+#include "test.h"
+#include "log_test_helpers.h"
+
+#include "or.h"
+#include "main.h"
+
+static void
+test_mainloop_update_time_normal(void *arg)
+{
+  (void)arg;
+
+  /* This time is in the past as of when this test was written. */
+  time_t now = 1525272090;
+  reset_uptime();
+  update_current_time(now);
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 0);
+
+  update_current_time(now); // Same time as before is a no-op.
+  tt_int_op(get_uptime(), OP_EQ, 0);
+
+  now += 1;
+  update_current_time(now);
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 1);
+
+  now += 2; // two-second jump is unremarkable.
+  update_current_time(now);
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 3);
+
+  now -= 1; // a one-second hop backwards is also unremarkable.
+  update_current_time(now);
+  tt_int_op(approx_time(), OP_EQ, now); // it changes the approx time...
+  tt_int_op(get_uptime(), OP_EQ, 3); // but it doesn't roll back our uptime
+
+ done:
+  ;
+}
+
+static void
+test_mainloop_update_time_jumps(void *arg)
+{
+  (void)arg;
+
+  /* This time is in the past as of when this test was written. */
+  time_t now = 220897152;
+  reset_uptime();
+  update_current_time(now);
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 0);
+
+  /* Put some uptime on the clock.. */
+  now += 3;
+  update_current_time(now);
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 3);
+
+  /* Now try jumping forward. */
+  setup_capture_of_logs(LOG_NOTICE);
+  now += 3600;
+  update_current_time(now);
+  expect_single_log_msg_containing(
+               "Your system clock just jumped 3600 seconds forward");
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 3); // no uptime change.
+  mock_clean_saved_logs();
+
+  now -= 600;
+  update_current_time(now);
+  expect_single_log_msg_containing(
+               "Your system clock just jumped 600 seconds backward");
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 3); // no uptime change.
+
+  /* uptime tracking should go normally now if the clock moves sensibly. */
+  now += 2;
+  update_current_time(now);
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 5);
+
+ done:
+  teardown_capture_of_logs();
+}
+
+#define MAINLOOP_TEST(name) \
+  { #name, test_mainloop_## name , TT_FORK, NULL, NULL }
+
+struct testcase_t mainloop_tests[] = {
+  MAINLOOP_TEST(update_time_normal),
+  MAINLOOP_TEST(update_time_jumps),
+  END_OF_TESTCASES
+};
+