♻️ refactor: Avoid running ixmp4 tests on Python 3.9

ixmp/backend/ixmp4.py

@@ -2,15 +2,11 @@
 from collections.abc import Generator, MutableMapping, Sequence
 from typing import TYPE_CHECKING, Any, Optional
 
-from ixmp4 import Platform
-from ixmp4.conf.base import PlatformInfo
-from ixmp4.data.backend import SqliteTestBackend
-from ixmp4.data.backend.base import Backend as ixmp4_backend
-
 from ixmp.backend.base import CachingBackend
 
 if TYPE_CHECKING:
     import ixmp4
+    from ixmp4.data.backend.base import Backend as ixmp4_backend
 
 log = logging.getLogger(__name__)
 
@@ -19,9 +15,13 @@ class IXMP4Backend(CachingBackend):
     """Backend using :mod:`ixmp4`."""
 
     _platform: "ixmp4.Platform"
-    _backend: ixmp4_backend
+    _backend: "ixmp4_backend"
+
+    def __init__(self, _backend: Optional["ixmp4_backend"] = None) -> None:
+        from ixmp4 import Platform
+        from ixmp4.conf.base import PlatformInfo
+        from ixmp4.data.backend import SqliteTestBackend
 
-    def __init__(self, _backend: Optional[ixmp4_backend] = None) -> None:
         # Create a default backend if None is provided
         if not _backend:
             log.warning("Falling back to default SqliteBackend 'ixmp4-local'")

ixmp/testing/__init__.py

@@ -35,6 +35,7 @@
 import logging
 import os
 import shutil
+import sys
 from collections.abc import Generator
 from contextlib import contextmanager, nullcontext
 from copy import deepcopy
@@ -45,8 +46,6 @@
 import pint
 import pytest
 from click.testing import CliRunner
-from ixmp4.conf.base import PlatformInfo
-from ixmp4.data.backend import SqliteTestBackend
 
 from ixmp import BACKENDS, Platform, cli
 from ixmp import config as ixmp_config
@@ -89,6 +88,12 @@
     "tmp_env",
 ]
 
+# Parametrize platforms for jdbc and ixmp4
+backends = list(BACKENDS.keys())
+# ixmp4 is not published for Python 3.9
+if sys.version_info < (3, 10):
+    backends.remove("ixmp4")
+
 
 # Pytest hooks
 
@@ -158,7 +163,7 @@ def test_data_path() -> Path:
     return Path(__file__).parents[1].joinpath("tests", "data")
 
 
-@pytest.fixture(scope="module", params=list(BACKENDS.keys()))
+@pytest.fixture(scope="module", params=backends)
 def test_mp(
     request: pytest.FixtureRequest, tmp_env, test_data_path
 ) -> Generator[Platform, Any, None]:
@@ -252,7 +257,7 @@ def protect_rename_dims():
     RENAME_DIMS.update(saved)
 
 
-@pytest.fixture(scope="function", params=list(BACKENDS.keys()))
+@pytest.fixture(scope="function", params=backends)
 def test_mp_f(request: pytest.FixtureRequest, tmp_env, test_data_path):
     """An empty :class:`Platform` connected to a temporary, in-memory database.
 
@@ -410,7 +415,8 @@ def _platform_fixture(
             platform_name, backend, "hsqldb", url=f"jdbc:hsqldb:mem:{platform_name}"
         )
     elif backend == "ixmp4":
-        # import ixmp4.conf
+        from ixmp4.conf.base import PlatformInfo
+        from ixmp4.data.backend import SqliteTestBackend
 
         # Setup ixmp4 backend and run DB migrations
         sqlite = SqliteTestBackend(

ixmp/tests/core/test_platform.py

@@ -2,6 +2,7 @@
 
 import logging
 import re
+import sys
 from sys import getrefcount
 from typing import TYPE_CHECKING
 from weakref import getweakrefcount
@@ -13,17 +14,21 @@
 
 import ixmp
 from ixmp.backend import FIELDS
-from ixmp.testing import DATA, assert_logs, models
+from ixmp.testing import DATA, assert_logs, backends, models
 
 if TYPE_CHECKING:
     from ixmp import Platform
 
+min_ixmp4_version = pytest.mark.skipif(
+    sys.version_info < (3, 10), reason="ixmp4 requires Python 3.10 or higher"
+)
+
 
 class TestPlatform:
     def test_init0(self):
         with pytest.raises(
             ValueError,
-            match=re.escape("backend class 'foo' not among ['ixmp4', 'jdbc']"),
+            match=re.escape(f"backend class 'foo' not among {backends}"),
         ):
             ixmp.Platform(backend="foo")
 
@@ -35,7 +40,7 @@ def test_init0(self):
         "backend, backend_args",
         (
             ("jdbc", dict(driver="hsqldb", url="jdbc:hsqldb:mem:TestPlatform")),
-            ("ixmp4", dict()),
+            pytest.param("ixmp4", dict(), marks=min_ixmp4_version),
         ),
     )
     def test_init1(self, backend, backend_args):