doc: add get_filtered_output method documentation

Add documentation for the get_filtered_output method in both the Python
implementation and the Integration with pytest chapter. The method is used
to filter command outputs by removing prompts and log messages, making it
easier to process shell command results.

Signed-off-by: Thomas Günther <thomas.guenther@limatica.com>

removed traling whitespace

doc/develop/test/pytest.rst

@@ -219,6 +219,8 @@ Shell
 
    .. automethod:: wait_for_prompt
 
+   .. automethod:: get_filtered_output
+
 
 Examples of pytest tests in the Zephyr project
 **********************************************

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

@@ -22,7 +22,9 @@ class Shell:
     Helper class that provides methods used to interact with shell application.
     """
 
-    def __init__(self, device: DeviceAdapter, prompt: str = 'uart:~$', timeout: float | None = None) -> None:
+    def __init__(
+        self, device: DeviceAdapter, prompt: str = 'uart:~$', timeout: float | None = None
+    ) -> None:
         self._device: DeviceAdapter = device
         self.prompt: str = prompt
         self.base_timeout: float = timeout or device.base_timeout
@@ -48,7 +50,9 @@ class Shell:
                 return True
         return False
 
-    def exec_command(self, command: str, timeout: float | None = None, print_output: bool = True) -> list[str]:
+    def exec_command(
+        self, command: str, timeout: float | None = None, print_output: bool = True
+    ) -> list[str]:
         """
         Send shell command to a device and return response. Passed command
         is extended by double enter sings - first one to execute this command
@@ -63,20 +67,42 @@ class Shell:
         self._device.write(command_ext.encode())
         lines: list[str] = []
         # wait for device command print - it should be done immediately after sending command to device
-        lines.extend(self._device.readlines_until(regex=regex_command, timeout=1.0, print_output=print_output))
+        lines.extend(
+            self._device.readlines_until(
+                regex=regex_command, timeout=1.0, print_output=print_output
+            )
+        )
         # wait for device command execution
-        lines.extend(self._device.readlines_until(regex=regex_prompt, timeout=timeout, print_output=print_output))
+        lines.extend(
+            self._device.readlines_until(
+                regex=regex_prompt, timeout=timeout, print_output=print_output
+            )
+        )
         return lines
 
     def get_filtered_output(self, command_lines: list[str]) -> list[str]:
+        """
+        Filter out prompts and log messages
+
+        Take the output of exec_command, which can contain log messages and command prompts,
+        and filter them to obtain only the command output.
+
+        Example:
+            >>> # equivalent to `lines = shell.exec_command("kernel version")`
+            >>> lines = [
+            >>>    'uart:~$',                    # filter prompts
+            >>>    'Zephyr version 3.6.0',       # keep this line
+            >>>    'uart:~$ <dbg> debug message' # filter log messages
+            >>> ]
+            >>> filtered_output = shell.get_filtered_output(output)
+            >>> filtered_output
+            ['Zephyr version 3.6.0']
+
+        :param command_lines: List of strings i.e. the output of `exec_command`.
+        :return: A list of strings containing, excluding prompts and log messages.
+        """
         regex_filter = re.compile(
-            '|'.join([
-                re.escape(self.prompt),
-                '<dbg>',
-                '<inf>',
-                '<wrn>',
-                '<err>'
-            ])
+            '|'.join([re.escape(self.prompt), '<dbg>', '<inf>', '<wrn>', '<err>'])
         )
         return list(filter(lambda l: not regex_filter.search(l), command_lines))
 
@@ -106,6 +132,7 @@ class ShellMCUbootCommandParsed:
     """
     Helper class to keep data from `mcuboot` shell command.
     """
+
     areas: list[ShellMCUbootArea] = field(default_factory=list)
 
     @classmethod