diff --git a/scripts/pylib/pytest-twister-harness/tests/conftest.py b/scripts/pylib/pytest-twister-harness/tests/conftest.py
index ed6b71287be..c221d4d2eba 100755
--- a/scripts/pylib/pytest-twister-harness/tests/conftest.py
+++ b/scripts/pylib/pytest-twister-harness/tests/conftest.py
@@ -6,14 +6,18 @@ from __future__ import annotations
 
 import os
 from pathlib import Path
+from typing import Generator
 
 import pytest
 
+from twister_harness.device.binary_adapter import NativeSimulatorAdapter
+from twister_harness.twister_harness_config import DeviceConfig
+
 
 @pytest.fixture
-def resources(request: pytest.FixtureRequest) -> Path:
-    """Return path to `data` folder"""
-    return Path(request.module.__file__).parent.joinpath('data')
+def resources() -> Path:
+    """Return path to `resources` folder"""
+    return Path(__file__).parent.joinpath('resources')
 
 
 @pytest.fixture
@@ -30,3 +34,24 @@ def twister_harness(zephyr_base) -> str:
     """Retrun path to pytest-twister-harness src directory"""
     pytest_twister_harness_path = str(Path(zephyr_base) / 'scripts' / 'pylib' / 'pytest-twister-harness' / 'src')
     return pytest_twister_harness_path
+
+
+@pytest.fixture
+def shell_simulator_path(resources: Path) -> str:
+    return str(resources / 'shell_simulator.py')
+
+
+@pytest.fixture
+def shell_simulator_adapter(
+    tmp_path: Path, shell_simulator_path: str
+) -> Generator[NativeSimulatorAdapter, None, None]:
+    build_dir = tmp_path / 'build_dir'
+    os.mkdir(build_dir)
+    device = NativeSimulatorAdapter(DeviceConfig(build_dir=build_dir, type='native', base_timeout=5.0))
+    try:
+        device.command = ['python3', shell_simulator_path]
+        device.launch()
+        yield device
+    finally:
+        device.write(b'quit\n')
+        device.close()
diff --git a/scripts/pylib/pytest-twister-harness/tests/device/binary_adapter_test.py b/scripts/pylib/pytest-twister-harness/tests/device/binary_adapter_test.py
index ab8b4d97d80..6103e2dac01 100755
--- a/scripts/pylib/pytest-twister-harness/tests/device/binary_adapter_test.py
+++ b/scripts/pylib/pytest-twister-harness/tests/device/binary_adapter_test.py
@@ -183,6 +183,18 @@ def test_if_binary_adapter_is_able_to_read_leftovers_after_disconnect_or_close(
     assert len(device.readlines()) > 0
 
 
+def test_if_binary_adapter_properly_send_data_to_subprocess(
+    shell_simulator_adapter: NativeSimulatorAdapter
+) -> None:
+    """Run shell_simulator.py program, send "zen" command and verify output."""
+    device = shell_simulator_adapter
+    time.sleep(0.1)
+    device.write(b'zen\n')
+    time.sleep(1)
+    lines = device.readlines_until(regex='Namespaces are one honking great idea')
+    assert 'The Zen of Python, by Tim Peters' in lines
+
+
 def test_if_native_binary_adapter_get_command_returns_proper_string(device: NativeSimulatorAdapter) -> None:
     device.generate_command()
     assert isinstance(device.command, list)
diff --git a/scripts/pylib/pytest-twister-harness/tests/device/hardware_adapter_test.py b/scripts/pylib/pytest-twister-harness/tests/device/hardware_adapter_test.py
index 24e120fc8ef..5655c4f3f72 100644
--- a/scripts/pylib/pytest-twister-harness/tests/device/hardware_adapter_test.py
+++ b/scripts/pylib/pytest-twister-harness/tests/device/hardware_adapter_test.py
@@ -3,6 +3,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 import os
+import time
 from pathlib import Path
 from unittest import mock
 
@@ -198,3 +199,21 @@ def test_if_hardware_adapter_uses_serial_pty(
 
     device.disconnect()
     assert not device._serial_pty_proc
+
+
+def test_if_hardware_adapter_properly_send_data_to_subprocess(
+    device: HardwareAdapter, shell_simulator_path: str
+) -> None:
+    """
+    Run shell_simulator.py under serial_pty, send "zen" command and verify
+    output. Flashing command is mocked by "dummy" echo command.
+    """
+    device.command = ['echo', 'TEST']  # only to mock flashing command
+    device.device_config.serial_pty = f'python3 {shell_simulator_path}'
+    device.launch()
+    time.sleep(0.1)
+    device.write(b'zen\n')
+    time.sleep(1)
+    lines = device.readlines_until(regex='Namespaces are one honking great idea')
+    assert 'The Zen of Python, by Tim Peters' in lines
+    device.write(b'quit\n')
diff --git a/scripts/pylib/pytest-twister-harness/tests/helpers/shell_test.py b/scripts/pylib/pytest-twister-harness/tests/helpers/shell_test.py
new file mode 100644
index 00000000000..1bab9380674
--- /dev/null
+++ b/scripts/pylib/pytest-twister-harness/tests/helpers/shell_test.py
@@ -0,0 +1,14 @@
+# Copyright (c) 2023 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: Apache-2.0
+
+from twister_harness.device.binary_adapter import NativeSimulatorAdapter
+from twister_harness.helpers.shell import Shell
+
+
+def test_if_shell_helper_properly_send_command(shell_simulator_adapter: NativeSimulatorAdapter) -> None:
+    """Run shell_simulator.py program, send "zen" command via shell helper and verify output."""
+    shell = Shell(shell_simulator_adapter, timeout=5.0)
+    assert shell.wait_for_prompt()
+    lines = shell.exec_command('zen')
+    assert 'The Zen of Python, by Tim Peters' in lines
diff --git a/scripts/pylib/pytest-twister-harness/tests/device/data/fifo_mock.py b/scripts/pylib/pytest-twister-harness/tests/resources/fifo_mock.py
similarity index 68%
rename from scripts/pylib/pytest-twister-harness/tests/device/data/fifo_mock.py
rename to scripts/pylib/pytest-twister-harness/tests/resources/fifo_mock.py
index b1d7f38e00b..da84716a1de 100755
--- a/scripts/pylib/pytest-twister-harness/tests/device/data/fifo_mock.py
+++ b/scripts/pylib/pytest-twister-harness/tests/resources/fifo_mock.py
@@ -9,29 +9,7 @@ import threading
 import time
 from argparse import ArgumentParser
 
-content = """
-The Zen of Python, by Tim Peters
-
-Beautiful is better than ugly.
-Explicit is better than implicit.
-Simple is better than complex.
-Complex is better than complicated.
-Flat is better than nested.
-Sparse is better than dense.
-Readability counts.
-Special cases aren't special enough to break the rules.
-Although practicality beats purity.
-Errors should never pass silently.
-Unless explicitly silenced.
-In the face of ambiguity, refuse the temptation to guess.
-There should be one-- and preferably only one --obvious way to do it.
-Although that way may not be obvious at first unless you're Dutch.
-Now is better than never.
-Although never is often better than *right* now.
-If the implementation is hard to explain, it's a bad idea.
-If the implementation is easy to explain, it may be a good idea.
-Namespaces are one honking great idea -- let's do more of those!
-"""
+from zen_of_python import zen_of_python
 
 
 class FifoFile:
@@ -90,7 +68,7 @@ def main():
     logger.info('Start')
 
     with FifoFile(write_path, 'wb') as wf, FifoFile(read_path, 'rb'):
-        for line in content.split('\n'):
+        for line in zen_of_python:
             wf.write(f'{line}\n'.encode('utf-8'))
     time.sleep(1)  # give a moment for external programs to collect all outputs
     return 0
diff --git a/scripts/pylib/pytest-twister-harness/tests/device/data/mock_script.py b/scripts/pylib/pytest-twister-harness/tests/resources/mock_script.py
similarity index 55%
rename from scripts/pylib/pytest-twister-harness/tests/device/data/mock_script.py
rename to scripts/pylib/pytest-twister-harness/tests/resources/mock_script.py
index e009ff6b58b..15076518223 100755
--- a/scripts/pylib/pytest-twister-harness/tests/device/data/mock_script.py
+++ b/scripts/pylib/pytest-twister-harness/tests/resources/mock_script.py
@@ -10,29 +10,7 @@ import sys
 import time
 from argparse import ArgumentParser
 
-s = """
-The Zen of Python, by Tim Peters
-
-Beautiful is better than ugly.
-Explicit is better than implicit.
-Simple is better than complex.
-Complex is better than complicated.
-Flat is better than nested.
-Sparse is better than dense.
-Readability counts.
-Special cases aren't special enough to break the rules.
-Although practicality beats purity.
-Errors should never pass silently.
-Unless explicitly silenced.
-In the face of ambiguity, refuse the temptation to guess.
-There should be one-- and preferably only one --obvious way to do it.
-Although that way may not be obvious at first unless you're Dutch.
-Now is better than never.
-Although never is often better than *right* now.
-If the implementation is hard to explain, it's a bad idea.
-If the implementation is easy to explain, it may be a good idea.
-Namespaces are one honking great idea -- let's do more of those!
-"""
+from zen_of_python import zen_of_python
 
 
 def main() -> int:
@@ -50,12 +28,12 @@ def main() -> int:
 
     if args.long_sleep:
         # prints data and wait for certain time
-        for line in s.split('\n'):
+        for line in zen_of_python:
             print(line, flush=True)
         time.sleep(args.sleep)
     else:
         # prints lines with delay
-        for line in s.split('\n'):
+        for line in zen_of_python:
             print(line, flush=True)
             time.sleep(args.sleep)
 
diff --git a/scripts/pylib/pytest-twister-harness/tests/resources/shell_simulator.py b/scripts/pylib/pytest-twister-harness/tests/resources/shell_simulator.py
new file mode 100644
index 00000000000..e0a1eb17896
--- /dev/null
+++ b/scripts/pylib/pytest-twister-harness/tests/resources/shell_simulator.py
@@ -0,0 +1,31 @@
+# Copyright (c) 2023 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: Apache-2.0
+
+"""
+Simple shell simulator.
+"""
+import sys
+
+from zen_of_python import zen_of_python
+
+PROMPT = 'uart:~$ '
+
+
+def main() -> int:
+    print('Start shell simulator', flush=True)
+    print(PROMPT, end='', flush=True)
+    for line in sys.stdin:
+        line = line.strip()
+        print(line, flush=True)
+        if line == 'quit':
+            break
+        elif line == 'zen':
+            for zen_line in zen_of_python:
+                print(zen_line, flush=True)
+
+        print(PROMPT, end='', flush=True)
+
+
+if __name__ == '__main__':
+    main()
diff --git a/scripts/pylib/pytest-twister-harness/tests/resources/zen_of_python.py b/scripts/pylib/pytest-twister-harness/tests/resources/zen_of_python.py
new file mode 100644
index 00000000000..7416e6ed2dc
--- /dev/null
+++ b/scripts/pylib/pytest-twister-harness/tests/resources/zen_of_python.py
@@ -0,0 +1,29 @@
+# Copyright (c) 2023 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: Apache-2.0
+
+from __future__ import annotations
+
+zen_of_python: list[str] = """
+The Zen of Python, by Tim Peters
+
+Beautiful is better than ugly.
+Explicit is better than implicit.
+Simple is better than complex.
+Complex is better than complicated.
+Flat is better than nested.
+Sparse is better than dense.
+Readability counts.
+Special cases aren't special enough to break the rules.
+Although practicality beats purity.
+Errors should never pass silently.
+Unless explicitly silenced.
+In the face of ambiguity, refuse the temptation to guess.
+There should be one-- and preferably only one --obvious way to do it.
+Although that way may not be obvious at first unless you're Dutch.
+Now is better than never.
+Although never is often better than *right* now.
+If the implementation is hard to explain, it's a bad idea.
+If the implementation is easy to explain, it may be a good idea.
+Namespaces are one honking great idea -- let's do more of those!
+""".split('\n')