Originally reported by: Anselm Kruis (Bitbucket: akruis, GitHub: akruis)

Problem

Since change e5a2ecca2b08 Stackless initializes the stackless subsystem only if application code loads the module stackless. This causes undefined behaviour in the C-Python test suite, if the execution order of the tests gets randomized. Especially some pickling tests are sensitive, because the initialisation of Stackless enables the pickling of additional types.

I observed failures especially with 3.5-slp, but the problem exists in all 3.x branches.

Proposed Solution

I'll import stackless in the module test.support. Nearly every test-module imports this module very early. While I'm at it, I'll also unify the tests for stackless being available.

• Bitbucket: https://bitbucket.org/stackless-dev/stackless/issue/126