[#372] Added decorator wait until stabilization metric values

Signed-off-by: Ilyas Niyazov <i.niyazov@yadro.com>

src/frostfs_testlib/storage/dataclasses/metrics.py

@@ -1,3 +1,9 @@
+import time
+from functools import wraps
+from typing import Callable
+
+import pytest
+
 from frostfs_testlib.hosting import Host
 from frostfs_testlib.shell.interfaces import CommandResult
 
@@ -7,11 +13,11 @@ class Metrics:
         self.storage = StorageMetrics(host, metrics_endpoint)
 
 
-
 class StorageMetrics:
     """
     Class represents storage metrics in a cluster
     """
+
     def __init__(self, host: Host, metrics_endpoint: str) -> None:
         self.host = host
         self.metrics_endpoint = metrics_endpoint
@@ -34,3 +40,41 @@ class StorageMetrics:
         shell = self.host.get_shell()
         result = shell.exec(f"curl -s {self.metrics_endpoint}")
         return result
+
+
+def wait_until_metric_result_is_stable(
+    relative_deviation: float = None, absolute_deviation: int = None, max_attempts: int = 10, sleep_interval: int = 30
+):
+    """
+    A decorator function that repeatedly calls the decorated function until its result stabilizes
+    within a specified relative tolerance or until the maximum number of attempts is reached.
+
+    This decorator is useful for scenarios where a function returns a metric or value that may fluctuate
+    over time, and you want to ensure that the result has stabilized before proceeding.
+    """
+
+    def decorator(func: Callable):
+        @wraps(func)
+        def wrapper(*args, **kwargs):
+            last_result = None
+            for _ in range(max_attempts):
+                # first function call
+                first_result = func(*args, **kwargs)
+
+                # waiting before the second call
+                time.sleep(sleep_interval)
+
+                # second function call
+                last_result = func(*args, **kwargs)
+
+                # checking value stability
+                if first_result == pytest.approx(last_result, rel=relative_deviation, abs=absolute_deviation):
+                    return last_result
+
+            # if stability is not achieved, return the last value
+            if last_result is not None:
+                return last_result
+
+        return wrapper
+
+    return decorator