qa: assert_raises_message() - search in str(e)

repr() is annoying because it requires escaping special characters, use str() instead.

Original discussion: https://github.com/bitcoin/bitcoin/pull/30660#discussion_r2080292165

test/functional/feature_framework_startup_failures.py

@@ -69,10 +69,10 @@ class FeatureFrameworkStartupFailures(BitcoinTestFramework):
         self.log.info("Verifying _verify_startup_failure() functionality (self-check).")
         assert_raises_message(
             AssertionError,
-            ("Child test didn't contain (only) expected errors:\n" +
+            ( "Child test didn't contain (only) expected errors:\n"
-             linesep.join(["Found 0/1 tracebacks - expecting exactly one with no knock-on exceptions.",
+             f"Found 0/1 tracebacks - expecting exactly one with no knock-on exceptions.{linesep}"
-                           "Found 0/1 occurrences of the specific exception: NonExistentError",
+             f"Found 0/1 occurrences of the specific exception: NonExistentError{linesep}"
-                           "Found 0/1 test failure output messages."])).encode("unicode_escape").decode("utf-8"),
+              "Found 0/1 test failure output messages."),
             self._verify_startup_failure,
             TestSuccess, [],
             "NonExistentError",

test/functional/test_framework/util.py

@@ -101,9 +101,9 @@ def assert_raises_message(exc, message, fun, *args, **kwds):
     except JSONRPCException:
         raise AssertionError("Use assert_raises_rpc_error() to test RPC failures")
     except exc as e:
-        if message is not None and message not in repr(e):
+        if message is not None and message not in str(e):
             raise AssertionError("Expected substring not found in exception:\n"
-                                 f"substring: '{message}'\nexception: {repr(e)}.")
+                                 f"substring: '{message}'\nexception: {e!r}.")
     except Exception as e:
         raise AssertionError("Unexpected exception raised: " + type(e).__name__)
     else: