diff --git a/tests/test_subshells.py b/tests/test_subshells.py
index 42082276..f119a787 100644
--- a/tests/test_subshells.py
+++ b/tests/test_subshells.py
@@ -40,19 +40,26 @@ def list_subshell_helper(kc: BlockingKernelClient):
     return reply["content"]
 
 
-def execute_request_subshell_id(kc: BlockingKernelClient, code: str, subshell_id: str | None):
+def execute_request_subshell_id(
+    kc: BlockingKernelClient, code: str, subshell_id: str | None, terminator: str = "\n"
+):
     msg = kc.session.msg("execute_request", {"code": code})
     msg["header"]["subshell_id"] = subshell_id
     msg_id = msg["msg_id"]
     kc.shell_channel.send(msg)
+    stdout = ""
     while True:
         msg = kc.get_iopub_msg()
-        # Get the stream message corresponding to msg_id
-        if msg["msg_type"] == "stream" and msg["parent_header"]["msg_id"] == msg_id:
-            content = msg["content"]
-            # assert content["name"] == "stdout"
-            break
-    return content["text"].strip()
+        # Get the stream messages corresponding to msg_id
+        if (
+            msg["msg_type"] == "stream"
+            and msg["parent_header"]["msg_id"] == msg_id
+            and msg["content"]["name"] == "stdout"
+        ):
+            stdout += msg["content"]["text"]
+            if stdout.endswith(terminator):
+                break
+    return stdout.strip()
 
 
 def execute_thread_count(kc: BlockingKernelClient) -> int:
@@ -118,15 +125,53 @@ def test_thread_ids():
         delete_subshell_helper(kc, subshell_id)
 
 
+@pytest.mark.parametrize("are_subshells", [(False, True), (True, False), (True, True)])
+@pytest.mark.parametrize("overlap", [True, False])
+def test_run_concurrently_sequence(are_subshells, overlap):
+    with kernel() as kc:
+        subshell_ids = [
+            create_subshell_helper(kc)["subshell_id"] if is_subshell else None
+            for is_subshell in are_subshells
+        ]
+        if overlap:
+            codes = [
+                "import time; start0=True; end0=False; time.sleep(0.2); end0=True",
+                "assert start0; assert not end0; time.sleep(0.2); assert end0",
+            ]
+        else:
+            codes = [
+                "import time; start0=True; end0=False; time.sleep(0.2); assert end1",
+                "assert start0; assert not end0; end1=True",
+            ]
+
+        msgs = []
+        for subshell_id, code in zip(subshell_ids, codes):
+            msg = kc.session.msg("execute_request", {"code": code})
+            msg["header"]["subshell_id"] = subshell_id
+            kc.shell_channel.send(msg)
+            msgs.append(msg)
+            if len(msgs) == 1:
+                time.sleep(0.1)  # Wait for first execute_request to start.
+
+        replies = get_replies(kc, [msg["msg_id"] for msg in msgs])
+
+        for subshell_id in subshell_ids:
+            if subshell_id:
+                delete_subshell_helper(kc, subshell_id)
+
+        for reply in replies:
+            assert reply["content"]["status"] == "ok"
+
+
 @pytest.mark.parametrize("include_main_shell", [True, False])
-def test_run_concurrently(include_main_shell):
+def test_run_concurrently_timing(include_main_shell):
     with kernel() as kc:
         subshell_ids = [
             None if include_main_shell else create_subshell_helper(kc)["subshell_id"],
             create_subshell_helper(kc)["subshell_id"],
         ]
 
-        times = (0.05, 0.05)
+        times = (0.2, 0.2)
         # Prepare messages, times are sleep times in seconds.
         # Identical times for both subshells is a harder test as preparing and sending
         # the execute_reply messages may overlap.
@@ -145,14 +190,18 @@ def test_run_concurrently(include_main_shell):
         _ = get_replies(kc, [msg["msg_id"] for msg in msgs])
         end = datetime.now()
 
-        duration = end - start
-        assert duration >= timedelta(seconds=max(times))
-        assert duration < timedelta(seconds=sum(times))
-
         for subshell_id in subshell_ids:
             if subshell_id:
                 delete_subshell_helper(kc, subshell_id)
 
+        duration = end - start
+        assert duration >= timedelta(seconds=max(times))
+        # Care is needed with this test as runtime conditions such as gathering
+        # coverage can slow it down causing the following assert to fail.
+        # The sleep time of 0.2 is empirically determined to run OK in CI, but
+        # consider increasing it if the following fails.
+        assert duration < timedelta(seconds=sum(times))
+
 
 def test_execution_count():
     with kernel() as kc:
@@ -173,12 +222,12 @@ def test_execution_count():
         # Wait for replies, may be in any order.
         replies = get_replies(kc, [msg["msg_id"] for msg in msgs])
 
+        delete_subshell_helper(kc, subshell_id)
+
         execution_counts = [r["content"]["execution_count"] for r in replies]
         ec = execution_counts[0]
         assert execution_counts == [ec, ec - 1, ec + 2, ec + 1]
 
-        delete_subshell_helper(kc, subshell_id)
-
 
 def test_create_while_execute():
     with kernel() as kc:
diff --git a/tests/utils.py b/tests/utils.py
index c7acbae9..b20e8fcb 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -75,15 +75,13 @@ def get_replies(kc, msg_ids: list[str], timeout=TIMEOUT, channel="shell"):
     t0 = time()
     count = 0
     replies = [None] * len(msg_ids)
-    while True:
+    while count < len(msg_ids):
         get_msg = getattr(kc, f"get_{channel}_msg")
         reply = get_msg(timeout=timeout)
         try:
             msg_id = reply["parent_header"]["msg_id"]
             replies[msg_ids.index(msg_id)] = reply
             count += 1
-            if count == len(msg_ids):
-                break
         except ValueError:
             # Allow debugging ignored replies
             print(f"Ignoring reply not to any of {msg_ids}: {reply}")