From e9ab4c5b271bac3215a25aa7adea84b6942839e1 Mon Sep 17 00:00:00 2001
From: Kefu Chai <kefu.chai@scylladb.com>
Date: Tue, 20 Jun 2023 11:35:49 +0800
Subject: [PATCH] tools/assertions: fail if exception does not match

before this change, we fail the test if repr(e) does *not* match
with the given `matching` regular expression. despite that the
tests pass as expected, this is what we intend to complete with
this verification. let's explain this with a Python REPL session:

```
>>> import re
>>> ex = Exception('foobarhello')
>>> matching = 'foobar'
>>> regex = re.compile(matching)
>>> actual = repr(e)
>>> actual
"Exception('foobarhello')"
>>> regex.match(actual) is None
True
>>> regex.match("c'est la vie") is None
True
```

`repr()` returns a canonical string representation of an object.
that's why it adds "Exception()" around the error message. and, it fails
to match with the the "matching" string. as "Exception('foobarhello')"
does not match at the beginning of this string. but we actually expect
the unmatch! in other words, two negatives make a positive.

to correct this, in this change:

* use str() to stringify the exception, so Python does not include its
  type in the output string
* do not check if the return match object is None, but check if it is
  *not* None. so the test can fail if the message string in exception
  does not match.
* include the message string and regular expression in the raised
  AssertionError.
* instead of using 're.match()', use 're.search()' for matching the
  regular expression with the message extracted from exception, as
  sometimes, we just pass a part of message in hope to match with
  the returned message, even if the part is not sitting at the beginning
  of the message, for instance, the full message looks like:
  ```
  Cannot execute this query as it might involve data filtering and thus
  may have unpredictable performance. If you want to execute this query
  despite the performance unpredictability, use ALLOW FILTERING'
  ````
  but we just use "use ALLOW FILTERING". so instead of changing all
  the tests, update the assert helper.
* do not compile the re. otherwise we only match it for a single
  time, and then drop the compiled re on the floor.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
---
 tools/assertions.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/assertions.py b/tools/assertions.py
index 78fd4444d3..ab50649939 100644
--- a/tools/assertions.py
+++ b/tools/assertions.py
@@ -55,8 +55,8 @@ def _assert_exception(fun, *args, **kwargs):
             fun(*args)
     except expected as e:
         if matching is not None:
-            regex = re.compile(matching)
-            assert regex.match(repr(e)) is None
+            msg = str(e)
+            assert re.search(matching, msg), f"Raised exception '{msg}' failed to match with '{matching}'"
     except Exception as e:
         raise e
     else: