twister: pytest: Fix shell fixture

On the hardware, after booting up the device, on the
console might appear additional logs after receiving first
prompt. Wait and clear the buffer to avoid unexpected
messages when verifying output.

Signed-off-by: Grzegorz Chwierut <grzegorz.chwierut@nordicsemi.no>

scripts/pylib/pytest-twister-harness/src/twister_harness/fixtures.py

@@ -6,6 +6,7 @@ import logging
 from typing import Generator, Type
 
 import pytest
+import time
 
 from twister_harness.device.device_adapter import DeviceAdapter
 from twister_harness.device.factory import DeviceFactory
@@ -58,7 +59,13 @@ def shell(dut: DeviceAdapter) -> Shell:
     """Return ready to use shell interface"""
     shell = Shell(dut, timeout=20.0)
     logger.info('Wait for prompt')
-    assert shell.wait_for_prompt()
+    if not shell.wait_for_prompt():
+        pytest.fail('Prompt not found')
+    if dut.device_config.type == 'hardware':
+        # after booting up the device, there might appear additional logs
+        # after first prompt, so we need to wait and clear the buffer
+        time.sleep(0.5)
+        dut.clear_buffer()
     return shell
 
 

scripts/pylib/pytest-twister-harness/src/twister_harness/helpers/shell.py

@@ -45,8 +45,6 @@ class Shell:
                 continue
             if self.prompt in line:
                 logger.debug('Got prompt')
-                time.sleep(0.05)
-                self._device.clear_buffer()
                 return True
         return False