Add integration tests

[michael-simons]

From sql2cypher created by lukaseder: neo4j-contrib/sql2cypher#23

It's probably not the top priority, but eventually, might be reasonable to think about integration tests, e.g. using testcontainers:
https://www.testcontainers.org/modules/databases/neo4j/

For this, it might be reasonable to compare the neo4j translated behaviour e.g. with H2?

The problems that the current test suite won't cover:

• Correct query semantics (e.g. when nesting / correlating stuff, there are always hairy edge cases)
• Data type conversion, etc.
• Other things?

[michael-simons]

Great idea.

Which free relational DB is best for a cleanest SQL standard? H2 / MySQL / Postgres?

[michael-simons]

I'd use H2 for this, it's become very standards compliant.