Thread

1. change regexp_substr first argument make tests more easier to understand.

   jian he <jian.universality@gmail.com> — 2023-12-27T16:13:14Z

   hi.
   https://git.postgresql.org/cgit/postgresql.git/tree/src/test/regress/expected/strings.out#n928
   
   SELECT regexp_substr('abcabcabc', 'a.c');
   SELECT regexp_substr('abcabcabc', 'a.c', 2);
   SELECT regexp_substr('abcabcabc', 'a.c', 1, 3);
   SELECT regexp_substr('abcabcabc', 'a.c', 1, 4) IS NULL AS t;
   SELECT regexp_substr('abcabcabc', 'A.C', 1, 2, 'i');
   
   they all return 'abc', there are 3 'abc ' in  string 'abcabcabc'
   except IS NULL query.
   maybe we can change regexp_substr first argument from "abcabcabc" to
   "abcaXcaYc".
   so the result would be more easier to understand.
   
   
   
   

2. Re: change regexp_substr first argument make tests more easier to understand.

   jian he <jian.universality@gmail.com> — 2023-12-28T07:17:00Z

   On Thu, Dec 28, 2023 at 12:13 AM jian he <jian.universality@gmail.com> wrote:
   >
   > hi.
   > https://git.postgresql.org/cgit/postgresql.git/tree/src/test/regress/expected/strings.out#n928
   >
   > SELECT regexp_substr('abcabcabc', 'a.c');
   > SELECT regexp_substr('abcabcabc', 'a.c', 2);
   > SELECT regexp_substr('abcabcabc', 'a.c', 1, 3);
   > SELECT regexp_substr('abcabcabc', 'a.c', 1, 4) IS NULL AS t;
   > SELECT regexp_substr('abcabcabc', 'A.C', 1, 2, 'i');
   >
   > they all return 'abc', there are 3 'abc ' in  string 'abcabcabc'
   > except IS NULL query.
   > maybe we can change regexp_substr first argument from "abcabcabc" to
   > "abcaXcaYc".
   > so the result would be more easier to understand.
   
   anyway here is the minor patch to  change string from "abcabcabc" to
   "abcaXcaYc".
   

3. Re: change regexp_substr first argument make tests more easier to understand.

   Tomas Vondra <tomas.vondra@enterprisedb.com> — 2024-07-18T21:49:16Z

   Hi,
   
   If I understand correctly, the problem is that it's not clear which of
   the 'abc' substrings is matched/returned by the function, right?
   
   I wonder if this is a problem only for understanding the test, or if it
   makes the tests a bit weaker. I mean, what if the function returns the
   wrong substring? How would we know?
   
   Also, if we tweak this, shouldn't we tweak also the regext_instr() calls
   a bit earlier in the test script?
   
   
   regards
   
   -- 
   Tomas Vondra
   EnterpriseDB: http://www.enterprisedb.com
   The Enterprise PostgreSQL Company
   
   
   
   

4. Re: change regexp_substr first argument make tests more easier to understand.

   jian he <jian.universality@gmail.com> — 2024-07-26T00:00:00Z

   On Fri, Jul 19, 2024 at 5:49 AM Tomas Vondra
   <tomas.vondra@enterprisedb.com> wrote:
   >
   > Hi,
   >
   > If I understand correctly, the problem is that it's not clear which of
   > the 'abc' substrings is matched/returned by the function, right?
   >
   > I wonder if this is a problem only for understanding the test, or if it
   > makes the tests a bit weaker. I mean, what if the function returns the
   > wrong substring? How would we know?
   >
   
   this is for understanding the test.
   personally, sometimes, I feel the documentation is too dry, hard to follow.
   so i can based on regress tests better understand the documentation.
   that was my intention for the changes.
   
   
   we have more sophisticated regex test at
   https://git.postgresql.org/cgit/postgresql.git/tree/src/test/modules/test_regex
   
   > Also, if we tweak this, shouldn't we tweak also the regext_instr() calls
   > a bit earlier in the test script?
   >
   sure.
   please check attached.
   

5. Re: change regexp_substr first argument make tests more easier to understand.

   Ilia Evdokimov <ilya.evdokimov@tantorlabs.com> — 2024-08-13T09:40:00Z

   Hi everybody
   
   Current tests with regexp_instr() and regexp_substr()  with string 
   'abcabcabc' are really unreadable and you would spend time to understand 
   that happens in these tests and if they are really correct. I'd better 
   change them into "abcdefghi" just like in query
   
        SELECT regexp_substr('abcdefghi', 'd.q') IS NULL AS t;
   
   Regards
   
   Ilia Evdokimov,
   Tantor Labs LLC.
   
   
   
   
   
   
   

6. Re: change regexp_substr first argument make tests more easier to understand.

   Tom Lane <tgl@sss.pgh.pa.us> — 2024-09-05T17:45:29Z

   Ilia Evdokimov <ilya.evdokimov@tantorlabs.com> writes:
   > Current tests with regexp_instr() and regexp_substr()  with string 
   > 'abcabcabc' are really unreadable and you would spend time to understand 
   > that happens in these tests and if they are really correct. I'd better 
   > change them into "abcdefghi" just like in query
   
   >      SELECT regexp_substr('abcdefghi', 'd.q') IS NULL AS t;
   
   On looking more closely at these test cases, I think the point of them
   is exactly to show the behavior of the functions with multiple copies
   of the target substring.  Thus, what Jian is proposing breaks the
   tests: it's no longer perfectly clear whether the result is because
   the function did what we expect, or because the pattern failed to
   match anywhere else.  (Sure, "a.c" *should* match "aXc", but if it
   didn't, you wouldn't discover that from this test.)  What Ilia
   proposes would break them worse.
   
   I think we should just reject this patch, or at least reject the
   parts of it that change existing test cases.  I have no opinion
   about whether the new test cases add anything useful.
   
   			regards, tom lane