Add consistency tests

This is one of those helpful situations where we have two
implementations of the same logic that should have exactly the same
result, so we can feed it any arbitrary input and test that the two are
consistent.

This is very useful for PEP 399 compliance.

Author: pganssle

Diff for: tests/test_zoneinfo_property.py

@@ -1,4 +1,5 @@
 import contextlib
+import datetime
 import os
 import pickle
 import unittest
@@ -175,3 +176,49 @@ def test_nocache(self, key):
 
 class CZoneInfoCacheTest(ZoneInfoCacheTest):
     klass = c_zoneinfo.ZoneInfo
+
+
+class PythonCConsistencyTest(unittest.TestCase):
+    """Tests that the C and Python versions do the same thing."""
+
+    @hypothesis.given(dt=hypothesis.strategies.datetimes(), key=valid_keys())
+    def test_same_str(self, dt, key):
+        py_dt = dt.replace(tzinfo=py_zoneinfo.ZoneInfo(key))
+        c_dt = dt.replace(tzinfo=c_zoneinfo.ZoneInfo(key))
+
+        self.assertEqual(str(py_dt), str(c_dt))
+
+    @hypothesis.given(dt=hypothesis.strategies.datetimes(), key=valid_keys())
+    def test_same_offsets_and_names(self, dt, key):
+        py_dt = dt.replace(tzinfo=py_zoneinfo.ZoneInfo(key))
+        c_dt = dt.replace(tzinfo=c_zoneinfo.ZoneInfo(key))
+
+        self.assertEqual(py_dt.tzname(), c_dt.tzname())
+        self.assertEqual(py_dt.utcoffset(), c_dt.utcoffset())
+        self.assertEqual(py_dt.dst(), c_dt.dst())
+
+    @hypothesis.given(
+        dt=hypothesis.strategies.datetimes(
+            timezones=hypothesis.strategies.just(datetime.timezone.utc)
+        ),
+        key=valid_keys(),
+    )
+    def test_same_from_utc(self, dt, key):
+        py_dt = dt.astimezone(py_zoneinfo.ZoneInfo(key))
+        c_dt = dt.astimezone(c_zoneinfo.ZoneInfo(key))
+
+        self.assertEqual(py_dt, c_dt)  # This is probably trivially true
+
+        self.assertEqual(py_dt.tzname(), c_dt.tzname())
+        self.assertEqual(py_dt.utcoffset(), c_dt.utcoffset())
+        self.assertEqual(py_dt.dst(), c_dt.dst())
+
+    @hypothesis.given(dt=hypothesis.strategies.datetimes(), key=valid_keys())
+    def test_same_to_utc(self, dt, key):
+        py_dt = dt.replace(tzinfo=py_zoneinfo.ZoneInfo(key))
+        c_dt = dt.replace(tzinfo=c_zoneinfo.ZoneInfo(key))
+
+        py_utc = py_dt.astimezone(datetime.timezone.utc)
+        c_utc = c_dt.astimezone(datetime.timezone.utc)
+
+        self.assertEqual(py_utc, c_utc)