I tried your steps and it didn't crash here either. I'll try to find a reproducible set of steps.
I isolated the test that was failing and it didn't fail by itself, so there is some interaction with my other tests. I tried running all tests in my laptop and yeap, it segfaults here too. So we can add "Ubuntu 18.04.4" with this Postgres:
```
# select version();
version
-----------------------------------------------------------------------------------------------------------------------------------
PostgreSQL 11.7 (Ubuntu 11.7-2.pgdg18.04+1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0, 64-bit
```
PG Bug reporting form <noreply@postgresql.org> writes:
> I finally found the issue was that one of the tests was trying to insert a
> row on a partitioned table, but there was no partition where to put that
> row, so it had to go to the default partition. But, the default partition
> had a constraint that disallowed that row, so the row couldn't be inserted
> and Postgres ended with a segfault.
Hm, works for me:
regression=# create table tt (f1 int, f2 text) partition by list(f1);
CREATE TABLE
regression=# create table t1 partition of tt for values in (1);
CREATE TABLE
regression=# create table tother partition of tt default;
CREATE TABLE
regression=# alter table tother add check (length(f2) > 1);
ALTER TABLE
regression=# insert into tt values (1, 'f');
INSERT 0 1
regression=# insert into tt values (3, 'f');
ERROR: new row for relation "tother" violates check constraint "tother_f2_check"
DETAIL: Failing row contains (3, f).
regression=#
Admittedly this is v11 branch tip not exactly 11.7, but I don't see
anything related-looking in the commit log. So I think there is some
contributing factor you didn't mention. Could you provide a
self-contained reproduction script?
regards, tom lane