SQ -> Tests: Shell: _read_until: Rewrite to no longer use sleep() and…

… polling, preferring select() instead

src/crystal/tests/test_shell.py

@@ -789,6 +789,9 @@ def _read_until(
     try:
         delta_time = 0.0
         while True:
+            # 1. Wait for stream to be ready to read or hit EOF
+            # 2. Read stream (if became ready)
+            # 3. Look for an acceptable `stop_suffix` at the end of everything read so far
             remaining_time = hard_timeout - delta_time
             assert remaining_time > 0
             (rlist_ready, _, xlist_ready) = select(
@@ -797,17 +800,27 @@ def _read_until(
                 [stream],
                 remaining_time)
             did_time_out = (len(rlist_ready) + len(xlist_ready) == 0)
-            if not did_time_out:
-                # NOTE: Quadratic performance.
+            if did_time_out:
+                # Look for an acceptable "stop suffix"
+                # Special case: '' is always an acceptable `stop_suffix`
+                if '' in stop_suffix_bytes_choices:
+                    found_stop_suffix = ''
+            else:
+                # Read stream
+                # NOTE: Append uses quadratic performance.
                 #       Not using for large amounts of text so I don't care.
                 read_buffer += stream.buffer.read1(1024)  # type: ignore[attr-defined]  # arbitrary
 
+                # Look for an acceptable "stop suffix"
                 for (i, s_bytes) in enumerate(stop_suffix_bytes_choices):
                     if read_buffer.endswith(s_bytes):
                         found_stop_suffix = stop_suffix[i]
                         break
-                if found_stop_suffix is not None:
-                    break
+            if found_stop_suffix is not None:
+                # Done
+                break
+
+            # If hard timeout exceeded then raise
             delta_time = time.time() - start_time
             if did_time_out or delta_time >= hard_timeout:
                 hard_timeout_exceeded = True
@@ -818,7 +831,7 @@ def _read_until(
                     f'Read so far: {read_so_far!r}',
                     read_so_far)
     finally:
-        # Warn if soft timeout exceeded
+        # If soft timeout exceeded then warn before returning
         if not hard_timeout_exceeded:
             delta_time = time.time() - start_time
             if delta_time > soft_timeout: