qa: Improve suppressed errors output

Original discussion: bitcoin/bitcoin#30660 (comment)

Author: hodlinator

test/functional/feature_framework_startup_failures.py

@@ -89,7 +89,7 @@ def run_test(self):
         self.log.info("Verifying inability to connect to bitcoind's RPC interface due to wrong port results in one exception containing at least one OSError.")
         self._verify_startup_failure(
             TestWrongRpcPortStartupFailure, [f"--internal_node_start_duration={node_start_duration}"],
-            r"AssertionError: \[node 0\] Unable to connect to bitcoind after \d+s \(ignored errors: {[^}]*'OSError \w+'?: \d+[^}]*}, latest error: \w+\([^)]+\)\)"
+            r"AssertionError: \[node 0\] Unable to connect to bitcoind after \d+s \(ignored errors: {[^}]*'OSError \w+'?: \d+[^}]*}, latest: '[\w ]+'/\w+\([^)]+\)\)"
         )
 
         self.log.info("Verifying startup failure due to invalid arg results in only one exception.")

test/functional/test_framework/test_node.py

@@ -263,8 +263,13 @@ def wait_for_rpc_connection(self, *, wait_for_import=True):
         """Sets up an RPC connection to the bitcoind process. Returns False if unable to connect."""
         # Poll at a rate of four times per second
         poll_per_s = 4
+
         suppressed_errors = collections.defaultdict(int)
-        latest_error = ""
+        latest_error = None
+        def suppress_error(category: str, e: Exception):
+            suppressed_errors[category] += 1
+            return (category, repr(e))
+
         for _ in range(poll_per_s * self.rpc_timeout):
             if self.process.poll() is not None:
                 # Attach abrupt shutdown error/s to the exception message
@@ -318,8 +323,7 @@ def wait_for_rpc_connection(self, *, wait_for_import=True):
                 # -342 Service unavailable, could be starting up or shutting down
                 if e.error['code'] not in [-28, -342]:
                     raise  # unknown JSON RPC exception
-                suppressed_errors[f"JSONRPCException {e.error['code']}"] += 1
-                latest_error = repr(e)
+                latest_error = suppress_error(f"JSONRPCException {e.error['code']}", e)
             except OSError as e:
                 error_num = e.errno
                 # Work around issue where socket timeouts don't have errno set.
@@ -335,16 +339,14 @@ def wait_for_rpc_connection(self, *, wait_for_import=True):
                     errno.ECONNREFUSED  # Port not yet open?
                 ]:
                     raise  # unknown OS error
-                suppressed_errors[f"OSError {errno.errorcode[error_num]}"] += 1
-                latest_error = repr(e)
+                latest_error = suppress_error(f"OSError {errno.errorcode[error_num]}", e)
             except ValueError as e:
                 # Suppress if cookie file isn't generated yet and no rpcuser or rpcpassword; bitcoind may be starting.
                 if "No RPC credentials" not in str(e):
                     raise
-                suppressed_errors["missing_credentials"] += 1
-                latest_error = repr(e)
+                latest_error = suppress_error("missing_credentials", e)
             time.sleep(1.0 / poll_per_s)
-        self._raise_assertion_error(f"Unable to connect to bitcoind after {self.rpc_timeout}s (ignored errors: {str(dict(suppressed_errors))}, latest error: {latest_error})")
+        self._raise_assertion_error(f"Unable to connect to bitcoind after {self.rpc_timeout}s (ignored errors: {dict(suppressed_errors)!s}{'' if latest_error is None else f', latest: {latest_error[0]!r}/{latest_error[1]}'})")
 
     def wait_for_cookie_credentials(self):
         """Ensures auth cookie credentials can be read, e.g. for testing CLI with -rpcwait before RPC connection is up."""