Use CrateDB test layer based on "Testcontainers", in order to improve platform coverage

[amotl]

Goal

Extend platform / operating system coverage when testing CrateDB and associated infrastructure.

Introduction

At Testcontainers for Java and CrateDB, we demonstrate how to run integration tests of Java applications with CrateDB, based on Testcontainers for Java.

Based on observations at GH-343, crate/crate-python#388, or mfussenegger/cr8#337, we experience problems with different hand-made test layers for CrateDB, written in Python. They may have their advantages, but are not platform agnostic, so they can't be used on macOS and Windows platforms without further ado.

Currently, the integration tests here are only being invoked on Linux.

crash/tests/test_integration.py

Lines 28 to 29 in 623ffb3

	if sys.platform != "linux":
	raise SkipTest("Integration tests only supported on Linux")

Proposal

On behalf of two other projects, we started the corresponding Testcontainers for Python implementation, and converged it into the cratedb-toolkit package, to make it reusable by downstream packages like crash, crate-python, and others.

• Testing: Improve "Testcontainers for Python" implementation cratedb-toolkit#57

This issue outlines what is needed to make the test layer usable here.

• Testing: Adapt "Testcontainers" implementation to unittest cratedb-toolkit#58

Task

Use the unittest-based adapter conceived to resolve crate/cratedb-toolkit#58 here, instead of crate.testing.layer in crash's tests/test_integration.py. Contributions are very welcome.

[amotl]

I think this has been implemented well by @pilosus with GH-408 (thank you again), so we could validate and possibly close this ticket.