Merge bitcoin#23136: test: update fee rate assertion helper in the fu…

…nctional test framework

b658d7d test: update assert_fee_amount() in test_framework/util.py (Jon Atack)

Pull request description:

  Follow-up to 42e1b5d (bitcoin#12486).
  - update call to `round()` with our utility function `satoshi_round()` to avoid intermittent test failures
  - rename `fee_per_kB` to `feerate_BTC_kvB` for precision
  - store division result in `feerate_BTC_vB`

  Possibly resolves bitcoin#19418.

ACKs for top commit:
  meshcollider:
    utACK b658d7d

Tree-SHA512: f124ded98c913f98782dc047a85a05d3fdf5f0585041fa81129be562138f6261ec1bd9ee2af89729028277e75b591b0a7ad50244016c2b2fa935c6e400523183

test/functional/test_framework/util.py

@@ -34,13 +34,14 @@ def assert_approx(v, vexp, vspan=0.00001):
         raise AssertionError("%s > [%s..%s]" % (str(v), str(vexp - vspan), str(vexp + vspan)))
 
 
-def assert_fee_amount(fee, tx_size, fee_per_kB):
-    """Assert the fee was in range"""
-    target_fee = round(tx_size * fee_per_kB / 1000, 8)
+def assert_fee_amount(fee, tx_size, feerate_BTC_kvB):
+    """Assert the fee is in range."""
+    feerate_BTC_vB = feerate_BTC_kvB / 1000
+    target_fee = satoshi_round(tx_size * feerate_BTC_vB)
     if fee < target_fee:
         raise AssertionError("Fee of %s BTC too low! (Should be %s BTC)" % (str(fee), str(target_fee)))
     # allow the wallet's estimation to be at most 2 bytes off
-    if fee > (tx_size + 2) * fee_per_kB / 1000:
+    if fee > (tx_size + 2) * feerate_BTC_vB:
         raise AssertionError("Fee of %s BTC too high! (Should be %s BTC)" % (str(fee), str(target_fee)))