Add validate test for timezones

test/tz_test/validate.cpp

@@ -0,0 +1,60 @@
+#include "tz.h"
+#include <iostream>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+    auto& db = get_tzdb();
+    std::vector<std::string> names;
+    names.reserve(db.zones.size() + db.links.size());
+    for (auto& zone : db.zones)
+        names.push_back(zone.name());
+    for (auto& link : db.links)
+        names.push_back(link.name());
+    std::sort(names.begin(), names.end());
+    for (auto const& name : names)
+    {
+        std::cout << name << '\n';
+        auto z = locate_zone(name);
+        auto begin = day_point(jan/1/year::min()) + 0s;
+        auto end   = day_point(jan/1/2035) + 0s;
+        auto info = z->get_info(begin, tz::utc);
+        std::cout << "Initially:           ";
+        if (info.offset >= 0s)
+            std::cout << '+';
+        std::cout << make_time(info.offset);
+        if (info.save == 0min)
+            std::cout << " standard ";
+        else
+            std::cout << " daylight ";
+        std::cout << info.abbrev << '\n';
+        auto prev_offset = info.offset;
+        auto prev_abbrev = info.abbrev;
+        auto prev_save = info.save;
+        for (begin = info.end; begin < end; begin = info.end)
+        {
+            info = z->get_info(begin, tz::utc);
+            if (info.offset == prev_offset && info.abbrev == prev_abbrev &&
+                    info.save == prev_save)
+                continue;
+            auto dp = floor<days>(begin);
+            auto ymd = year_month_day(dp);
+            auto time = make_time(begin - dp);
+            std::cout << ymd << 'T' << time << "Z ";
+            if (info.offset >= 0s)
+                std::cout << '+';
+            std::cout << make_time(info.offset);
+            if (info.save == 0min)
+                std::cout << " standard ";
+            else
+                std::cout << " daylight ";
+            std::cout << info.abbrev << '\n';
+            prev_offset = info.offset;
+            prev_abbrev = info.abbrev;
+            prev_save = info.save;
+        }
+        std::cout << '\n';
+    }
+}