Housekeeping: make Postgres tests also run the H2-based tests

[paullatzelsperger]

Feature Request

For many SQL-implementations we have two test classes: one that uses H2, and one that uses an actual Postgres instance. This was done to enable the SQL test to run locally and very fast without an actual Postgres instance.

Due to to fact how JUnit Test tags work, the Postgres test cannot extend the H2 test, because then it would always run, even if the -DincludeTags="PostgresqlDbIntegrationTest" is not specified, thus requiring all developers to have a local Postgres instance.

We have observed on multiple occasions that bugs occur on Postgres, and not on H2, especially when using Postgres-specific features, such as the JSON datatype.

Which Areas Would Be Affected?

build, CI

Why Is the Feature Desired?

Test coverage, test consistency

Solution Proposal

There are basically two ways I can think of to solve this:

1. Move the actual test code into a "test method" class, and invoke all methods from the test classes:

   @Test
   void someTest(){
       testMethods.runSomeTest();
   }

   The upside is that test code is centrally located. The downside is that we still have to duplicate all test methods.
2. ditch H2, run everything on Postgres. The upside of this is that we always have realistic tests, don't need to run them twice. The downside is, that for locally running the test, users have to run Postgres and specify the -DincludeTags="PostgresqlDbIntegrationTest" flag

As a semi-related issue we could move all the Postgres initialization code into a JUnit PostgresExtension and add an @ExtendWith on the test class.

Type of Issue

cleanup

Checklist

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