[tests] Improve assert message when wait_until() fails

Author: jnewbery

test/functional/test_framework/util.py

@@ -8,6 +8,7 @@
 from binascii import hexlify, unhexlify
 from decimal import Decimal, ROUND_DOWN
 import hashlib
+import inspect
 import json
 import logging
 import os
@@ -204,9 +205,9 @@ def wait_until(predicate, *, attempts=float('inf'), timeout=float('inf'), lock=N
     if attempts == float('inf') and timeout == float('inf'):
         timeout = 60
     attempt = 0
-    timeout += time.time()
+    time_end = time.time() + timeout
 
-    while attempt < attempts and time.time() < timeout:
+    while attempt < attempts and time.time() < time_end:
         if lock:
             with lock:
                 if predicate():
@@ -218,8 +219,12 @@ def wait_until(predicate, *, attempts=float('inf'), timeout=float('inf'), lock=N
         time.sleep(0.05)
 
     # Print the cause of the timeout
-    assert_greater_than(attempts, attempt)
-    assert_greater_than(timeout, time.time())
+    predicate_source = inspect.getsourcelines(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')
 
 # RPC/P2P connection constants and functions