Kinda fix the C API tests

Lib/test/datetimetester.py

@@ -6384,14 +6384,18 @@ class IranTest(ZoneInfoTest):
 
 @unittest.skipIf(_testcapi is None, 'need _testcapi module')
 class CapiTest(unittest.TestCase):
+
     def setUp(self):
         # Since the C API is not present in the _Pure tests, skip all tests
         if self.__class__.__name__.endswith('Pure'):
             self.skipTest('Not relevant in pure Python')
 
         # This *must* be called, and it must be called first, so until either
         # restriction is loosened, we'll call it as part of test setup
-        _testcapi.test_datetime_capi()
+        _testcapi.setup_capi()
+
+    def tearDown(self):
+        _testcapi.teardown_capi()
 
     def test_utc_capi(self):
         for use_macro in (True, False):

Modules/_testcapi/datetime.c

@@ -6,26 +6,21 @@
 static int test_run_counter = 0;
 
 static PyObject *
-test_datetime_capi(PyObject *self, PyObject *args)
+setup_capi(PyObject *self, PyObject *args)
 {
-    if (PyDateTimeAPI) {
-        if (test_run_counter) {
-            /* Probably regrtest.py -R */
-            Py_RETURN_NONE;
-        }
-        else {
-            PyErr_SetString(PyExc_AssertionError,
-                            "PyDateTime_CAPI somehow initialized");
-            return NULL;
-        }
-    }
-    test_run_counter++;
-    PyDateTime_IMPORT;
-
-    if (PyDateTimeAPI) {
-        Py_RETURN_NONE;
+    if (!test_run_counter++) {
+        PyDateTime_IMPORT;
     }
-    return NULL;
+    assert(PyDateTimeAPI);
+    Py_RETURN_NONE;
+}
+
+static PyObject *
+teardown_capi(PyObject *self, PyObject *args)
+{
+    test_run_counter--;
+    assert(test_run_counter >= 0);
+    Py_RETURN_NONE;
 }
 
 /* Functions exposing the C API type checking for testing */
@@ -467,7 +462,8 @@ static PyMethodDef test_methods[] = {
     {"get_timezone_utc_capi",       get_timezone_utc_capi,          METH_VARARGS},
     {"get_timezones_offset_zero",   get_timezones_offset_zero,      METH_NOARGS},
     {"make_timezones_capi",         make_timezones_capi,            METH_NOARGS},
-    {"test_datetime_capi",          test_datetime_capi,             METH_NOARGS},
+    {"setup_capi",                  setup_capi,                     METH_NOARGS},
+    {"teardown_capi",               teardown_capi,                  METH_NOARGS},
     {NULL},
 };