Add pytest integration tests

[darwintree]

#2944

What is done

This pull request adds new integration written in pytest to simplify test , especially rpc test setup. The legacy python tests still exists.

Code Organization

• integration_tests/conflux/*: test framework helper code refactored from tests/conflux/* (simply code import path)
• integratioin_tests/test_framework/* test framework setup code refactored from tests/integration_tests/test_framework/*
  • tests/integration_tests/test_framework/test_framework.py was changed a lot in order to adapt the pytest test process. The original test entry main() is removed and its code is break down and moved into __init__ and teardown function. The teardown function will be called by pytest framework
• integration_tests/tests/*: new version integration tests. In */conftest.py, pytest fixtures are setup so they can be directly used by tests

How Parallel Testing Works

The pytest-xdist plugin enables tests running on different CPUs and in the tests we are using --dist loadscope to specify tests are distributed in modules (whereas each .py file). And in pytest fixtures, the fixture scope is set as scope="module". This means that tests within a module will be distributed to different CPUs and fixtures will be setup when the module tests starts and will be tear down after the module tests.

How Tests can be Migrated or Used

Check integration_tests/readme.md.

What all Tests be Migrated to the New One

I think no, at least not all, as there is not a must for the migration.

However, rpc tests can be migrated to the new test framework as there is a plan to add more rpc tests under the new test framework. And migration would make it easier to review and check if any edge case were missed

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