Add tests for wxDateTime setters around DST end time

Check that setting the other date components doesn't change its hour.

See https://github.com/wxWidgets/wxWidgets/pull/367

tests/datetime/datetimetest.cpp

@@ -1586,4 +1586,54 @@ void DateTimeTestCase::TestConvToFromLocalTZ()
     CPPUNIT_ASSERT_EQUAL( dt.ToTimezone(wxDateTime::Local), dt );
 }
 
+static void DoTestSetFunctionsOnDST(const wxDateTime &orig)
+{
+#define DST_TEST_FUN(func) \
+    { \
+        wxDateTime copy = orig; \
+        copy.func; \
+        CHECK(orig.IsDST() == copy.IsDST()); \
+        CHECK(orig.GetHour() == copy.GetHour()); \
+    }
+
+    // Test the functions by just calling them with their existing values
+    // This is primarily just ensuring that we're not converting to a Tm and back
+    // but also if we do that we're handling it properly
+    DST_TEST_FUN(SetMinute(orig.GetMinute()));
+    DST_TEST_FUN(SetSecond(orig.GetSecond()));
+    DST_TEST_FUN(SetMillisecond(orig.GetMillisecond()));
+    DST_TEST_FUN(SetDay(orig.GetDay()));
+    DST_TEST_FUN(SetMonth(orig.GetMonth()));
+    DST_TEST_FUN(SetYear(orig.GetYear()));
+
+    // Test again by actually changing the time (this shouldn't affect DST)
+    // Can't test changing the date because that WILL affect DST
+    DST_TEST_FUN(SetMinute((orig.GetMinute() + 1) % 60));
+    DST_TEST_FUN(SetSecond((orig.GetSecond() + 1) % 60));
+    DST_TEST_FUN(SetMillisecond((orig.GetMillisecond() + 1) % 1000));
+
+    {
+        // Special case for set hour since it's ambiguous at DST we don't care if IsDST matches
+        wxDateTime copy = orig;
+        copy.SetHour(orig.GetHour());
+        CHECK(orig.GetHour() == copy.GetHour());
+    }
+#undef DST_TEST_FUN
+}
+
+TEST_CASE("wxDateTime::SetOnDST", "[datetime][dst]")
+{
+    wxDateTime dst = wxDateTime::GetEndDST();
+    if ( !dst.IsValid() )
+    {
+        WARN("Skipping test as DST period couldn't be determined.");
+        return;
+    }
+
+    // End DST is the 2nd 1am after DST ends so go back an hour to the first 1am
+    DoTestSetFunctionsOnDST(dst - wxTimeSpan::Hour());
+
+    DoTestSetFunctionsOnDST(dst);
+}
+
 #endif // wxUSE_DATETIME