Merge bitcoin/bitcoin#30893: test: Introduce ensure_for helper

111465d72d test: Remove unused attempts parameter from wait_until (Fabian Jahr)
5468a23eb9 test: Add check_interval parameter to wait_until (Fabian Jahr)
16c87d91fd test: Introduce ensure_for helper (Fabian Jahr)

Pull request description:

  A repeating pattern in the functional tests is that the test sleeps for a while to ensure that a certain condition is still true after some amount of time has elapsed. Most recently a new case of this was added in #30807. This PR here introduces an `ensure` helper to streamline this functionality.

  Some approach considerations:
  - It is possible to construct this by reusing `wait_until` and wrapping it in `try` internally. However, the logger output of the failing wait would still be printed which seems irritating. So I opted for simplified but similar internals to `wait_until`.
  - This implementation starts for a failure in the condition right away which has the nice side-effect that it might give feedback on a failure earlier than is currently the case. However, in some cases, it may be expected that the condition may still be false at the beginning and then turns true until time has run out, something that would work when the test sleeps without checking in a loop. I decided against this design (and even against adding it as an option) because such a test design seems like it would be racy either way.
  - I have also been going back and forth on naming. To me `ensure` works well but I am also not a native speaker, happy consider a different name if others don't think it's clear enough.

ACKs for top commit:
  maflcko:
    re-ACK 111465d72d 🍋
  achow101:
    ACK 111465d72d
  tdb3:
    code review re ACK 111465d72d
  furszy:
    utACK 111465d72d

Tree-SHA512: ce01a4f3531995375a6fbf01b27d51daa9d4c3d7cd10381be6e86ec5925d2965861000f7cb4796b8d40aabe3b64c4c27e2811270e4e3c9916689575b8ba4a2aa

test/functional/test_framework/util.py

@@ -268,7 +268,28 @@ def satoshi_round(amount: Union[int, float, str], *, rounding: str) -> Decimal:
     return Decimal(amount).quantize(SATOSHI_PRECISION, rounding=rounding)
 
 
-def wait_until_helper_internal(predicate, *, attempts=float('inf'), timeout=float('inf'), lock=None, timeout_factor=1.0):
+def ensure_for(*, duration, f, check_interval=0.2):
+    """Check if the predicate keeps returning True for duration.
+
+    check_interval can be used to configure the wait time between checks.
+    Setting check_interval to 0 will allow to have two checks: one in the
+    beginning and one after duration.
+    """
+    # If check_interval is 0 or negative or larger than duration, we fall back
+    # to checking once in the beginning and once at the end of duration
+    if check_interval <= 0 or check_interval > duration:
+        check_interval = duration
+    time_end = time.time() + duration
+    predicate_source = "''''\n" + inspect.getsource(f) + "'''"
+    while True:
+        if not f():
+            raise AssertionError(f"Predicate {predicate_source} became false within {duration} seconds")
+        if time.time() > time_end:
+            return
+        time.sleep(check_interval)
+
+
+def wait_until_helper_internal(predicate, *, timeout=60, lock=None, timeout_factor=1.0, check_interval=0.05):
     """Sleep until the predicate resolves to be True.
 
     Warning: Note that this method is not recommended to be used in tests as it is
@@ -277,13 +298,10 @@ def wait_until_helper_internal(predicate, *, attempts=float('inf'), timeout=floa
     properly scaled. Furthermore, `wait_until()` from `P2PInterface` class in
     `p2p.py` has a preset lock.
     """
-    if attempts == float('inf') and timeout == float('inf'):
-        timeout = 60
     timeout = timeout * timeout_factor
-    attempt = 0
     time_end = time.time() + timeout
 
-    while attempt < attempts and time.time() < time_end:
+    while time.time() < time_end:
         if lock:
             with lock:
                 if predicate():
@@ -291,17 +309,12 @@ def wait_until_helper_internal(predicate, *, attempts=float('inf'), timeout=floa
         else:
             if predicate():
                 return
-        attempt += 1
-        time.sleep(0.05)
+        time.sleep(check_interval)
 
     # Print the cause of the timeout
     predicate_source = "''''\n" + inspect.getsource(predicate) + "'''"
     logger.error("wait_until() failed. Predicate: {}".format(predicate_source))
-    if attempt >= attempts:
-        raise AssertionError("Predicate {} not true after {} attempts".format(predicate_source, attempts))
-    elif time.time() >= time_end:
-        raise AssertionError("Predicate {} not true after {} seconds".format(predicate_source, timeout))
-    raise RuntimeError('Unreachable')
+    raise AssertionError("Predicate {} not true after {} seconds".format(predicate_source, timeout))
 
 
 def sha256sum_file(filename):