So, there is some historical context as to why it is a separate test suite.
And some of the differences are specific to Greenplum -- e.g. needing to connect
to a specific database in "utility mode" to do something.
However, the other differences are actually pretty handy and would be applicable
to upstream as well.
We use a different syntax than the isolation framework and have some nice
features. Most notably, explicit control over blocking.
The syntax for what would be a "step" in isolation is like this:
[<#>[flag]:] <sql> | ! <shell scripts or command>
where # is the session number and flags include the following:
&: expect blocking behavior
>: running in background without blocking
<: join an existing session
q: quit the given session
See the script [1] for parsing the test cases for more details on the syntax and
capabilities (it is in Python).
[1]
https://github.com/greenplum-db/gpdb/blob/master/src/test/isolation2/sql_isolation_testcase.py