Make ndb.eventloop private. (#6392)

Make eventloop private.

Makes ndb.eventloop private by renaming to ndb._eventloop. Addresses #6376 .

ndb/MIGRATION_NOTES.md

@@ -83,6 +83,9 @@ The primary differences come from:
   Now `Property._FIND_METHODS_CACHE` is set to `{}` when the `Property` class
   is created and there is another level of keys (based on fully-qualified
   class name) in the cache.
+- `eventloop` has been renamed to `_eventloop`. It is believed that `eventloop`
+  was previously a *de facto* private module, so we've just made that
+  explicit.
 
 ## Comments
 

ndb/tests/unit/test_eventloop.py → ndb/tests/unit/test__eventloop.py

@@ -17,7 +17,7 @@
 
 import pytest
 
-from google.cloud.ndb import eventloop
+from google.cloud.ndb import _eventloop as eventloop
 import tests.unit.utils
 
 
@@ -125,15 +125,15 @@ def test_queue_call_now(self):
         assert list(loop.current) == [("foo", ("bar",), {"baz": "qux"})]
         assert not loop.queue
 
-    @unittest.mock.patch("google.cloud.ndb.eventloop.time")
+    @unittest.mock.patch("google.cloud.ndb._eventloop.time")
     def test_queue_call_soon(self, time):
         loop = self._make_one()
         time.time.return_value = 5
         loop.queue_call(5, "foo", "bar", baz="qux")
         assert not loop.current
         assert loop.queue == [_Event(10, "foo", ("bar",), {"baz": "qux"})]
 
-    @unittest.mock.patch("google.cloud.ndb.eventloop.time")
+    @unittest.mock.patch("google.cloud.ndb._eventloop.time")
     def test_queue_call_absolute(self, time):
         loop = self._make_one()
         time.time.return_value = 5
@@ -217,7 +217,7 @@ def test_run0_idler(self):
         assert loop.run0() == 0
         callback.assert_called_once_with("foo", bar="baz")
 
-    @unittest.mock.patch("google.cloud.ndb.eventloop.time")
+    @unittest.mock.patch("google.cloud.ndb._eventloop.time")
     def test_run0_next_later(self, time):
         time.time.return_value = 0
         callback = unittest.mock.Mock(__name__="callback")
@@ -229,7 +229,7 @@ def test_run0_next_later(self, time):
         assert len(loop.queue) == 1
         assert loop.inactive == 88
 
-    @unittest.mock.patch("google.cloud.ndb.eventloop.time")
+    @unittest.mock.patch("google.cloud.ndb._eventloop.time")
     def test_run0_next_now(self, time):
         time.time.return_value = 0
         callback = unittest.mock.Mock(__name__="callback")
@@ -253,7 +253,7 @@ def test_run1_nothing_to_do(self):
         loop = self._make_one()
         assert loop.run1() is False
 
-    @unittest.mock.patch("google.cloud.ndb.eventloop.time")
+    @unittest.mock.patch("google.cloud.ndb._eventloop.time")
     def test_run1_has_work_now(self, time):
         callback = unittest.mock.Mock(__name__="callback")
         loop = self._make_one()
@@ -262,7 +262,7 @@ def test_run1_has_work_now(self, time):
         time.sleep.assert_not_called()
         callback.assert_called_once_with()
 
-    @unittest.mock.patch("google.cloud.ndb.eventloop.time")
+    @unittest.mock.patch("google.cloud.ndb._eventloop.time")
     def test_run1_has_work_later(self, time):
         time.time.return_value = 0
         callback = unittest.mock.Mock(__name__="callback")
@@ -272,7 +272,7 @@ def test_run1_has_work_later(self, time):
         time.sleep.assert_called_once_with(5)
         callback.assert_not_called()
 
-    @unittest.mock.patch("google.cloud.ndb.eventloop.time")
+    @unittest.mock.patch("google.cloud.ndb._eventloop.time")
     def test_run(self, time):
         time.time.return_value = 0