Add comments indicating when dependency check can be removed

Author: kevin-bates

notebook/notebookapp.py

@@ -1392,10 +1392,10 @@ def init_configurables(self):
         )
         #  Ensure the appropriate version of Python and jupyter_client is available.
         if isinstance(self.kernel_manager, AsyncMappingKernelManager):
-            if sys.version_info < (3, 6):
+            if sys.version_info < (3, 6):  # Can be removed once 3.5 is dropped.
                 raise ValueError("You are using `AsyncMappingKernelManager` in Python 3.5 (or lower) "
                                  "which is not supported. Please upgrade Python to 3.6+ or change kernel managers.")
-            if not async_kernel_mgmt_available:
+            if not async_kernel_mgmt_available:  # Can be removed once jupyter_client >= 6.1 is required.
                 raise ValueError("You are using `AsyncMappingKernelManager` without an appropriate "
                                  "jupyter_client installed!  Please upgrade jupyter_client or change kernel managers.")
             self.log.info("Asynchronous kernel management has been configured to use '{}'.".

notebook/services/kernels/tests/test_kernels_api.py

@@ -201,9 +201,9 @@ class AsyncKernelAPITest(KernelAPITest):
 
     @classmethod
     def setup_class(cls):
-        if not async_testing_enabled:
+        if not async_testing_enabled:  # Can be removed once jupyter_client >= 6.1 is required.
             raise SkipTest("AsyncKernelAPITest tests skipped due to down-level jupyter_client!")
-        if sys.version_info < (3, 6):
+        if sys.version_info < (3, 6):  # Can be removed once 3.5 is dropped.
             raise SkipTest("AsyncKernelAPITest tests skipped due to Python < 3.6!")
         super(AsyncKernelAPITest, cls).setup_class()
 

notebook/services/sessions/tests/test_sessions_api.py

@@ -271,9 +271,9 @@ class AsyncSessionAPITest(SessionAPITest):
 
     @classmethod
     def setup_class(cls):
-        if not async_testing_enabled:
+        if not async_testing_enabled:  # Can be removed once jupyter_client >= 6.1 is required.
             raise SkipTest("AsyncSessionAPITest tests skipped due to down-level jupyter_client!")
-        if sys.version_info < (3, 6):
+        if sys.version_info < (3, 6):  # Can be removed once 3.5 is dropped.
             raise SkipTest("AsyncSessionAPITest tests skipped due to Python < 3.6!")
         super(AsyncSessionAPITest, cls).setup_class()