Sync monitor issue when switching between reader and contributor role

[vxgmichel]

The following scenario fails:

diff --git a/tests/core/test_sync_monitor_stateful.py b/tests/core/test_sync_monitor_stateful.py
index fd29007f..b600ac1e 100644
--- a/tests/core/test_sync_monitor_stateful.py
+++ b/tests/core/test_sync_monitor_stateful.py
@@ -187,6 +187,7 @@ def test_sync_monitor_stateful(
                 await wfs.touch(file_path)
             else:
                 data = self.get_next_data()
+                assert await wfs.exists(file_path)
                 await wfs.write_bytes(file_path, data)
             await wfs.sync()
 
@@ -203,8 +204,8 @@ def test_sync_monitor_stateful(
             else:
                 data = self.get_next_data()
                 try:
-                    if await wfs.exists(file_path):
-                        await wfs.write_bytes(file_path, data)
+                    assert await wfs.exists(file_path)
+                    await wfs.write_bytes(file_path, data)
                 except (FSWorkspaceNoAccess, OSError):
                     return
 
@@ -247,4 +248,19 @@ def test_sync_monitor_stateful(
             self.synced_files.update(new_synced_files)
             return multiple(*(sorted(new_synced_files)))
 
-    run_state_machine_as_test(SyncMonitorStateful, settings=hypothesis_settings)
+    from parsec.api.protocol import RealmRole
+    state = SyncMonitorStateful()
+
+    async def steps():
+        await state.init()
+        v1 = await state.create_sharing(RealmRole.CONTRIBUTOR)
+        await state.create_file(author=bob.device_id, wid=v1)
+        v2 = await state.let_core_monitors_process_changes()
+        await state.update_file(author=alice.device_id, file=v2.values[0])
+        await state.update_sharing(new_role=RealmRole.READER, wid=v1)
+        await state.update_sharing(new_role=RealmRole.CONTRIBUTOR, wid=v1)
+        await state.let_core_monitors_process_changes()
+        await state.teardown()
+    state.trio_run(steps)
+
+    # run_state_machine_as_test(SyncMonitorStateful, settings=hypothesis_settings)

Trace:

../../miniconda/envs/parsec/lib/python3.7/site-packages/hypothesis_trio/stateful.py:293: in _trio_main_afn
    await corofn(*args)
tests/core/test_sync_monitor_stateful.py:262: in steps
    await state.let_core_monitors_process_changes()
tests/core/test_sync_monitor_stateful.py:241: in let_core_monitors_process_changes
    recursive_compare_fs_dumps(alice_dump, bob_dump, ignore_need_sync=False)
tests/core/test_sync_monitor_stateful.py:46: in recursive_compare_fs_dumps
    recursive_compare_fs_dumps(alice_value, bob_value, ignore_need_sync=ignore_need_sync)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

alice_dump = {'base_version': 1, 'blocks': [[{'access': None, 'id': ChunkID('33fe6913-38ed-4394-af68-a0a31582b898'), 'raw_offset': 0, 'raw_size': 6, ...}]], 'blocksize': 524288, 'created': <Pendulum [2020-08-24T09:55:15.367170+00:00]>, ...}
bob_dump = {'base_version': 1, 'blocks': [], 'blocksize': 524288, 'created': <Pendulum [2020-08-24T09:55:15.367170+00:00]>, ...}
ignore_need_sync = False

    def recursive_compare_fs_dumps(alice_dump, bob_dump, ignore_need_sync=False):
        if ignore_need_sync and alice_dump.get("need_sync", False):
            return
    
        alice_stripped_dump = {}
        bob_stripped_dump = {}
        for field in TO_COMPARE_FIELDS:
            alice_value = alice_dump.get(field, MISSING)
            bob_value = bob_dump.get(field, MISSING)
            if alice_value is not MISSING and bob_value is not MISSING:
                alice_stripped_dump[field] = alice_value
                bob_stripped_dump[field] = bob_value
>       assert alice_stripped_dump == bob_stripped_dump
E       AssertionError: assert {'base_versio...': False, ...} == {'base_versio...': False, ...}
E         Omitting 4 identical items, use -vv to show
E         Differing items:
E         {'need_sync': True} != {'need_sync': False}
E         {'updated': <Pendulum [2020-08-24T09:55:15.488858+00:00]>} != {'updated': <Pendulum [2020-08-24T09:55:15.367170+00:00]>}
E         Use -v to get the full diff

tests/core/test_sync_monitor_stateful.py:38: AssertionError