gh-143959: Split datetime tests requiring _datetime

Lib/test/test_datetime.py

@@ -2,27 +2,40 @@
 import sys
 import functools
 
-from test.support.import_helper import import_fresh_module
+from test.support.import_helper import import_fresh_module, import_module
 
 
 TESTS = 'test.datetimetester'
 
 def load_tests(loader, tests, pattern):
     try:
-        pure_tests = import_fresh_module(TESTS,
-                                         fresh=['datetime', '_pydatetime', '_strptime'],
-                                         blocked=['_datetime'])
-        fast_tests = import_fresh_module(TESTS,
-                                         fresh=['datetime', '_strptime'],
-                                         blocked=['_pydatetime'])
+        pure_tests = import_fresh_module(
+            TESTS,
+            fresh=['datetime', '_pydatetime', '_strptime'],
+            blocked=['_datetime'],
+        )
+        fast_tests = None
+        try:
+            import_module('_datetime')
+        except ImportError:
+            fast_tests = None
+        else:
+            fast_tests = import_fresh_module(
+                TESTS,
+                fresh=['datetime', '_strptime'],
+                blocked=['_pydatetime'],
+            )
     finally:
         # XXX: import_fresh_module() is supposed to leave sys.module cache untouched,
         # XXX: but it does not, so we have to cleanup ourselves.
-        for modname in ['datetime', '_datetime', '_strptime']:
+        for modname in ['datetime', '_datetime', '_pydatetime', '_strptime']:
             sys.modules.pop(modname, None)
 
-    test_modules = [pure_tests, fast_tests]
-    test_suffixes = ["_Pure", "_Fast"]
+    test_modules = [pure_tests]
+    test_suffixes = ["_Pure"]
+    if fast_tests is not None:
+        test_modules.append(fast_tests)
+        test_suffixes.append("_Fast")
     # XXX(gb) First run all the _Pure tests, then all the _Fast tests.  You might
     # not believe this, but in spite of all the sys.modules trickery running a _Pure
     # test last will leave a mix of pure and native datetime stuff lying around.