Fix a few missing DeprecationWarnings in tests

In one test, we simply turn off DeprecationWarning rather than asserting
about it, because whether the error condition happens before or after
the warning seems to differ between the Python and C versions.

Lib/test/datetimetester.py

@@ -14,6 +14,7 @@
 import re
 import struct
 import unittest
+import warnings
 
 from array import array
 
@@ -51,7 +52,6 @@
 # mixed-type comparisons.
 OTHERSTUFF = (10, 34.5, "abc", {}, [], ())
 
-
 # XXX Copied from test_float.
 INF = float("inf")
 NAN = float("nan")
@@ -2649,9 +2649,10 @@ def test_utcfromtimestamp_limits(self):
         for test_name, ts in test_cases:
             with self.subTest(test_name, ts=ts):
                 with self.assertRaises((ValueError, OverflowError)):
-                    # converting a Python int to C time_t can raise a
-                    # OverflowError, especially on 32-bit platforms.
-                    self.theclass.utcfromtimestamp(ts)
+                    with self.assertWarns(DeprecationWarning):
+                        # converting a Python int to C time_t can raise a
+                        # OverflowError, especially on 32-bit platforms.
+                        self.theclass.utcfromtimestamp(ts)
 
     def test_insane_fromtimestamp(self):
         # It's possible that some platform maps time_t to double,
@@ -2668,8 +2669,9 @@ def test_insane_utcfromtimestamp(self):
         # exempt such platforms (provided they return reasonable
         # results!).
         for insane in -1e200, 1e200:
-            self.assertRaises(OverflowError, self.theclass.utcfromtimestamp,
-                              insane)
+            with self.assertWarns(DeprecationWarning):
+                self.assertRaises(OverflowError, self.theclass.utcfromtimestamp,
+                                  insane)
 
     @unittest.skipIf(sys.platform == "win32", "Windows doesn't accept negative timestamps")
     def test_negative_float_fromtimestamp(self):
@@ -3028,7 +3030,7 @@ def __new__(cls, *args, **kwargs):
         for name, meth_name, kwargs in test_cases:
             with self.subTest(name):
                 constr = getattr(DateTimeSubclass, meth_name)
-                if constr == "utcnow":
+                if meth_name == "utcnow":
                     with self.assertWarns(DeprecationWarning):
                         dt = constr(**kwargs)
                 else:
@@ -4756,8 +4758,10 @@ def test_tzinfo_utcfromtimestamp(self):
         # Try with and without naming the keyword; for whatever reason,
         # utcfromtimestamp() doesn't accept a tzinfo argument.
         off42 = FixedOffset(42, "42")
-        self.assertRaises(TypeError, meth, ts, off42)
-        self.assertRaises(TypeError, meth, ts, tzinfo=off42)
+        with warnings.catch_warnings(category=DeprecationWarning):
+            warnings.simplefilter("ignore", category=DeprecationWarning)
+            self.assertRaises(TypeError, meth, ts, off42)
+            self.assertRaises(TypeError, meth, ts, tzinfo=off42)
 
     def test_tzinfo_timetuple(self):
         # TestDateTime tested most of this.  datetime adds a twist to the