import downgrade test

rather than building old xeus-cling, which requires a downgrade of Python from 3.10 to 3.9,
which is _not_ supported,
run the build with a 3.9 pin.

This still results in patch-level downgrade of Python, major downgrade of openssl, etc.

Author: minrk

tests/conda/downgrade/environment.yml

@@ -0,0 +1,11 @@
+# originally [email protected]
+# added python=3.9 pin because implicit downgrade of Python from 3.10 to 3.9 isn't allowed
+name: xeus-cling
+channels:
+  - conda-forge
+dependencies:
+  - python=3.9
+  - xeus-cling=0.6.0
+  - xtensor=0.20.8
+  - xtensor-blas=0.16.1
+  - notebook

tests/conda/downgrade/verify

@@ -0,0 +1,30 @@
+#!/usr/bin/env python3
+import json
+import pprint
+from subprocess import check_output
+
+
+def json_sh(cmd):
+    """Run a command that produces JSON on stdout and return the parsed result"""
+    buf = check_output(cmd)
+    return json.loads(buf.decode("utf8", "replace"))
+
+
+conda_pkg_list = json_sh(["conda", "list", "--json"])
+pprint.pprint(conda_pkg_list)
+# make it a dict
+pkgs = {pkg["name"]: pkg for pkg in conda_pkg_list}
+
+# base env resolved
+assert pkgs["python"]["version"].startswith("3.9"), pkgs["python"]
+assert "xeus-cling" in pkgs
+assert pkgs["xeus-cling"]["version"] == "0.6.0"
+
+# verify downgrade
+# this may be brittle, but it's unlikely any of these old versions
+# of packages will be rebuilt
+# xeus-cling 0.6.0 pins xeus 0.20, which pins openssl 1.1.1,
+# which in turn downgrades Python from >=3.9.16 to 3.9.6
+
+assert pkgs["openssl"]["version"].startswith("1.1.1"), pkgs["openssl"]["version"]
+assert pkgs["python"]["version"] == "3.9.6", pkgs["python"]["version"]

tests/external/reproductions.repos.yaml

@@ -24,12 +24,6 @@
   url: https://github.com/binder-examples/requirements
   ref: python-3.7
   verify: python -c 'import matplotlib'
-# Test that custom channels and downgrades don't
-# get blocked by pinning
-- name: Xeus-Cling
-  url: https://github.com/QuantStack/xeus-cling
-  ref: 0.6.0
-  verify: jupyter kernelspec list
 # Zenodo record of https://github.com/binder-examples/requirements
 - name: 10.5281/zenodo.3242074
   url: 10.5281/zenodo.3242074