diff --git a/notebook/services/contents/fileio.py b/notebook/services/contents/fileio.py
index b9d38726a..003491194 100644
--- a/notebook/services/contents/fileio.py
+++ b/notebook/services/contents/fileio.py
@@ -171,8 +171,10 @@ class FileManagerMixin(Configurable):
     log : logging.Logger
     """
 
-    use_atomic_writing = Bool(True, config=True, help="""flag to deactivate
-            atomic writing on slow (like networked) file system.""")
+    use_atomic_writing = Bool(True, config=True, help=
+    """By default notebooks are saved on disk on a temporary file and then if succefully written, it replaces the old ones.
+      This procedure, namely 'atomic_writing', causes some bugs on file system whitout operation order enforcement (like some networked fs).
+      If set to False, the new notebook is written directly on the old one which could fail (eg: full filesystem or quota )""")
 
     @contextmanager
     def open(self, os_path, *args, **kwargs):
@@ -183,7 +185,9 @@ class FileManagerMixin(Configurable):
 
     @contextmanager
     def atomic_writing(self, os_path, *args, **kwargs):
-        """wrapper around atomic_writing that turns permission errors to 403"""
+        """wrapper around atomic_writing that turns permission errors to 403.
+        Depending on flag 'use_atomic_writing', the wrapper perform an actual atomic writing or
+        simply writes the file (whatever an old exists or not)"""
         with self.perm_to_403(os_path):
             if self.use_atomic_writing:
                 with atomic_writing(os_path, *args, log=self.log, **kwargs) as f:
diff --git a/notebook/services/contents/tests/test_manager.py b/notebook/services/contents/tests/test_manager.py
index 7b224e4f5..7954f6726 100644
--- a/notebook/services/contents/tests/test_manager.py
+++ b/notebook/services/contents/tests/test_manager.py
@@ -530,7 +530,10 @@ class TestContentsManager(TestCase):
         assert cm.notary.check_signature(nb)
 
 
-class TestContentsManagerNoAtomic(TestCase):
+class TestContentsManagerNoAtomic(TestContentsManager):
+    """
+    Make same test in no atomic case than in atomic case, using inheritance
+    """
 
     def setUp(self):
         self._temp_dir = TemporaryDirectory()
@@ -539,23 +542,3 @@ class TestContentsManagerNoAtomic(TestCase):
             root_dir = self.td,
         )
         self.contents_manager.use_atomic_writing = False
-
-    def tearDown(self):
-        self._temp_dir.cleanup()
-
-    def new_notebook_no_atomic(self):
-        """
-
-        """
-        cm = self.contents_manager
-        model = cm.new_untitled(type="notebook")
-        name = model['name']
-        path = model['path']
-
-        full_model = cm.get(path)
-        nb = full_model['content']
-        nb['metadata']['counter'] = int(1e6 * time.time())
-        self.add_code_cell(nb)
-
-        cm.save(full_model, path)
-        return nb, name, path