[improv_serial] Add uart bus support and host integration test (#18794)

tests/integration/log_utils.py

@@ -0,0 +1,43 @@
+"""Helpers for asserting on log output in integration tests."""
+
+from __future__ import annotations
+
+import asyncio
+
+
+class LineWaiter:
+    """Collects log lines and lets a test await one containing all needles.
+
+    Pass ``callback`` as ``run_compiled``'s ``line_callback``; the callback runs
+    on the test's own event loop, so futures are resolved directly. Only one
+    ``wait_for`` may be outstanding at a time (tests await sequentially).
+    """
+
+    def __init__(self) -> None:
+        self.lines: list[str] = []
+        self._needles: tuple[str, ...] = ()
+        self._future: asyncio.Future | None = None
+
+    def callback(self, line: str) -> None:
+        self.lines.append(line)
+        if (
+            self._future is not None
+            and not self._future.done()
+            and all(n in line for n in self._needles)
+        ):
+            self._future.set_result(line)
+            self._future = None
+
+    async def wait_for(self, *needles: str, timeout: float = 10.0) -> str:
+        """Return the first line, past or future, containing every needle."""
+        for line in self.lines:
+            if all(n in line for n in needles):
+                return line
+        assert self._future is None or self._future.done(), "concurrent wait_for"
+        self._needles = needles
+        self._future = asyncio.get_running_loop().create_future()
+        try:
+            return await asyncio.wait_for(self._future, timeout)
+        finally:
+            self._future = None
+            self._needles = ()