Additional testing for devtools client/server

tests/utilities/render.py

@@ -1,9 +1,11 @@
+import asyncio
 import io
 import re
+from typing import Callable
 
+import pytest
 from rich.console import Console, RenderableType
 
-
 re_link_ids = re.compile(r"id=[\d\.\-]*?;.*?\x1b")
 
 
@@ -23,3 +25,32 @@ def render(renderable: RenderableType, no_wrap: bool = False) -> str:
         console.print(renderable, no_wrap=no_wrap, end="")
     output = replace_link_ids(capture.get())
     return output
+
+
+async def wait_for_predicate(
+    predicate: Callable[[], bool],
+    timeout_secs: float = 2,
+    poll_delay_secs: float = 0.001,
+) -> None:
+    """Wait for the given predicate to become True by evaluating it every `poll_delay_secs`
+    seconds. Fail the pytest test if the predicate does not become True after `timeout_secs`
+    seconds.
+
+    Args:
+        predicate (Callable[[], bool]): The predicate function which will be called repeatedly.
+        timeout_secs (float): If the predicate doesn't evaluate to True after this number of
+            seconds, the test will fail.
+        poll_delay_secs (float): The number of seconds to wait between each call to the
+            predicate function.
+    """
+    time_taken = 0
+    while True:
+        result = predicate()
+        if result:
+            return
+        await asyncio.sleep(poll_delay_secs)
+        time_taken += poll_delay_secs
+        if time_taken > timeout_secs:
+            pytest.fail(
+                f"Predicate {predicate} did not return True after {timeout_secs} seconds."
+            )