[time] Test the year roll-over of increment_second and increment_day across 2100

tests/components/time/increment.cpp

@@ -0,0 +1,62 @@
+// Year roll-over in ESPTime::increment_second() and increment_day(): 2100 is a common year, 2000 and 2024 are leap
+// years, so the day of the year must wrap after 365 or 366 days accordingly.
+
+#include <gtest/gtest.h>
+#include "esphome/core/time.h"
+
+namespace esphome::testing {
+
+static ESPTime last_day_of(uint16_t year, uint16_t day_of_year) {
+  ESPTime t{};
+  t.second = 59;
+  t.minute = 59;
+  t.hour = 23;
+  t.day_of_week = 5;
+  t.day_of_month = 31;
+  t.day_of_year = day_of_year;
+  t.month = 12;
+  t.year = year;
+  return t;
+}
+
+static void expect_new_year(const ESPTime &t, uint16_t year) {
+  EXPECT_EQ(t.year, year);
+  EXPECT_EQ(t.month, 1);
+  EXPECT_EQ(t.day_of_month, 1);
+  EXPECT_EQ(t.day_of_year, 1);
+}
+
+TEST(ESPTimeIncrement, DayRollsOverCommonCenturyYear) {
+  ESPTime t = last_day_of(2100, 365);
+  t.increment_day();
+  expect_new_year(t, 2101);
+}
+
+TEST(ESPTimeIncrement, SecondRollsOverCommonCenturyYear) {
+  ESPTime t = last_day_of(2100, 365);
+  t.increment_second();
+  expect_new_year(t, 2101);
+  EXPECT_EQ(t.hour, 0);
+  EXPECT_EQ(t.minute, 0);
+  EXPECT_EQ(t.second, 0);
+}
+
+TEST(ESPTimeIncrement, DayRollsOverLeapYears) {
+  ESPTime t = last_day_of(2000, 366);
+  t.increment_day();
+  expect_new_year(t, 2001);
+  t = last_day_of(2024, 366);
+  t.increment_day();
+  expect_new_year(t, 2025);
+}
+
+TEST(ESPTimeIncrement, DayStaysInLeapYearOnDay365) {
+  ESPTime t = last_day_of(2024, 365);
+  t.day_of_month = 30;
+  t.increment_day();
+  EXPECT_EQ(t.year, 2024);
+  EXPECT_EQ(t.day_of_year, 366);
+  EXPECT_EQ(t.day_of_month, 31);
+}
+
+}  // namespace esphome::testing