diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index edfd56e..8f1291c 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -2478,23 +2478,32 @@
   call assert_fails('call job_start([0zff])', 'E976:')
 endfunc
 
-" Test for the 'lsp' channel mode
-func LspCb(chan, msg)
-  call add(g:lspNotif, a:msg)
-  if a:msg->has_key('method')
-    " Requests received from the LSP server
-    if a:msg['method'] == 'server-req-in-middle'
-          \ && a:msg['params']['text'] == 'server-req'
-      call ch_sendexpr(a:chan, #{method: 'server-req-in-middle-resp',
-            \ id: a:msg['id'], params: #{text: 'client-resp'}})
-    endif
+" Process requests received from the LSP server
+func LspProcessServerRequests(chan, msg)
+  if a:msg['method'] == 'server-req-in-middle'
+        \ && a:msg['params']['text'] == 'server-req'
+    call ch_sendexpr(a:chan, #{method: 'server-req-in-middle-resp',
+          \ id: a:msg['id'], params: #{text: 'client-resp'}})
   endif
 endfunc
 
-func LspOtCb(chan, msg)
-  call add(g:lspOtMsgs, a:msg)
+" LSP channel message callback function
+func LspCb(chan, msg)
+  call add(g:lspNotif, a:msg)
+  if a:msg->has_key('method')
+    call LspProcessServerRequests(a:chan, a:msg)
+  endif
 endfunc
 
+" LSP one-time message callback function (used for ch_sendexpr())
+func LspOtCb(chan, msg)
+  call add(g:lspOtMsgs, a:msg)
+  if a:msg->has_key('method')
+    call LspProcessServerRequests(a:chan, a:msg)
+  endif
+endfunc
+
+" Test for the 'lsp' channel mode
 func LspTests(port)
   " call ch_logfile('Xlspclient.log', 'w')
   let ch = ch_open(s:localhost .. a:port, #{mode: 'lsp', callback: 'LspCb'})
@@ -2661,7 +2670,7 @@
   call assert_equal('alive', ch_evalexpr(ch, #{method: 'ping'}).result)
 
   " Test for processing a request message from the server while the client
-  " is waiting for a response with the same identifier.
+  " is waiting for a response with the same identifier (sync-rpc)
   let g:lspNotif = []
   let resp = ch_evalexpr(ch, #{method: 'server-req-in-middle',
         \ params: #{text: 'client-req'}})
@@ -2673,6 +2682,44 @@
         \ #{id: 28, jsonrpc: '2.0', method: 'server-req-in-middle',
         \   params: #{text: 'server-req'}}], g:lspNotif)
 
+  " Test for processing a request message from the server while the client
+  " is waiting for a response with the same identifier (async-rpc using the
+  " channel callback function)
+  let g:lspNotif = []
+  call ch_sendexpr(ch, #{method: 'server-req-in-middle', id: 500,
+        \ params: #{text: 'client-req'}})
+  " Send three pings to wait for all the notification messages to arrive
+  for i in range(3)
+    call assert_equal('alive', ch_evalexpr(ch, #{method: 'ping'}).result)
+  endfor
+  call assert_equal([
+        \ #{id: -1, jsonrpc: '2.0', method: 'server-req-in-middle',
+        \   params: #{text: 'server-notif'}},
+        \ #{id: 500, jsonrpc: '2.0', method: 'server-req-in-middle',
+        \   params: #{text: 'server-req'}},
+        \ #{id: 500, jsonrpc: '2.0', result: #{text: 'server-resp'}}
+        \ ], g:lspNotif)
+
+  " Test for processing a request message from the server while the client
+  " is waiting for a response with the same identifier (async-rpc using a
+  " one-time callback function)
+  let g:lspNotif = []
+  let g:lspOtMsgs = []
+  call ch_sendexpr(ch, #{method: 'server-req-in-middle',
+        \ params: #{text: 'client-req'}}, #{callback: 'LspOtCb'})
+  " Send a ping to wait for all the notification messages to arrive
+  for i in range(3)
+    call assert_equal('alive', ch_evalexpr(ch, #{method: 'ping'}).result)
+  endfor
+  call assert_equal([
+        \ #{id: 32, jsonrpc: '2.0', result: #{text: 'server-resp'}}],
+        \ g:lspOtMsgs)
+  call assert_equal([
+        \ #{id: -1, jsonrpc: '2.0', method: 'server-req-in-middle',
+        \ params: #{text: 'server-notif'}},
+        \ #{id: 32, jsonrpc: '2.0', method: 'server-req-in-middle',
+        \ params: {'text': 'server-req'}}], g:lspNotif)
+
   " Test for invoking an unsupported method
   let resp = ch_evalexpr(ch, #{method: 'xyz', params: {}}, #{timeout: 200})
   call assert_equal({}, resp)