Make pytest use one process for CI

[glatterf42]

Using pytest-xdist is most likely causing flakiness in our test suite because some tests seem to write/read from processes they should not care about, leading to the common error messages listed below. While we ideally want to implement a more sustainable fix soon (e.g., making the names of the scenarios/processes unique), we don't want to spend a lot of time rerunning flaky tests manually in the meantime. So this PR makes pytest use just one process as a mitigation suggested by @khaeru.

Common error messages

FAILED ixmp/tests/test_tutorials.py::test_py_transport - nbclient.exceptions.CellExecutionError: An error occurred while executing the following cell:
------------------
# launch the ix modeling platform using the default back end
mp = ixmp.Platform()

# The following lines have the same effect:
# mp = ixmp.Platform(name='local')  # Default local database
# mp = ixmp.Platform(name='default')  # Default database -> 'local'
------------------


---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
File Platform.java:110, in at.ac.iiasa.ixmp.Platform.<init>()

File Platform.java:163, in at.ac.iiasa.ixmp.Platform.initPlatform()

File DbDAO.java:238, in at.ac.iiasa.ixmp.database.DbDAO.create()

File DbDAO.java:318, in at.ac.iiasa.ixmp.database.DbDAO.updateSchemaIfNecessary()

File Flyway.java:910, in org.flywaydb.core.Flyway.migrate()

File Flyway.java:1238, in org.flywaydb.core.Flyway.execute()

File Flyway.java:910, in org.flywaydb.core.Flyway$1.execute()

File Flyway.java:918, in org.flywaydb.core.Flyway$1.execute()

File Flyway.java:78, in org.flywaydb.core.Flyway.access$100()

File Flyway.java:1037, in org.flywaydb.core.Flyway.doValidate()

Exception: Java Exception

The above exception was the direct cause of the following exception:

org.flywaydb.core.api.FlywayException     Traceback (most recent call last)
File ~/hostedtoolcache/Python/3.8.18/x64/lib/python3.8/site-packages/ixmp/backend/jdbc.py:297, in JDBCBackend.__init__(self, jvmargs, **kwargs)
    296 try:
--> 297     self.jobj = java.Platform("Python", properties)
    298 except java.NoClassDefFoundError as e:  # pragma: no cover

org.flywaydb.core.api.FlywayException: org.flywaydb.core.api.FlywayException: Validate failed: Detected failed migration to version 1 (hsql base version)

During handling of the above exception, another exception occurred:

RuntimeError                              Traceback (most recent call last)
Cell In[2], line 2
      1 # launch the ix modeling platform using the default back end
----> 2 mp = ixmp.Platform()
      4 # The following lines have the same effect:
      5 # mp = ixmp.Platform(name='local')  # Default local database
      6 # mp = ixmp.Platform(name='default')  # Default database -> 'local'

File ~/hostedtoolcache/Python/3.8.18/x64/lib/python3.8/site-packages/ixmp/core/platform.py:94, in Platform.__init__(self, name, backend, **backend_args)
     88     raise ValueError(
     89         f"backend class {repr(backend_class_name)} not among "
     90         + str(sorted(BACKENDS.keys()))
     91     )
     93 # Instantiate the backend
---> 94 self._backend = backend_class(**kwargs)

File ~/hostedtoolcache/Python/3.8.18/x64/lib/python3.8/site-packages/ixmp/backend/jdbc.py:320, in JDBCBackend.__init__(self, jvmargs, **kwargs)
    318     else:
    319         _raise_jexception(e)
--> 320     raise RuntimeError(f"{msg}\n(Java: {jclass})")
    322 # Set the log level
    323 self.set_log_level(log_level)

RuntimeError: when initializing database:
(Java: org.flywaydb.core.api.FlywayException)
On: macos-latest-py3.8, macos-latest-py3.10

FAILED ixmp/tests/test_tutorials.py::test_py_transport_scenario - nbclient.exceptions.CellExecutionError: An error occurred while executing the following cell:
------------------
# launch the ix modeling platform using the default local database
mp = ixmp.Platform()
------------------


---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
File Platform.java:110, in at.ac.iiasa.ixmp.Platform.<init>()

File Platform.java:163, in at.ac.iiasa.ixmp.Platform.initPlatform()

File DbDAO.java:238, in at.ac.iiasa.ixmp.database.DbDAO.create()

File DbDAO.java:318, in at.ac.iiasa.ixmp.database.DbDAO.updateSchemaIfNecessary()

File Flyway.java:910, in org.flywaydb.core.Flyway.migrate()

File Flyway.java:1238, in org.flywaydb.core.Flyway.execute()

File Flyway.java:910, in org.flywaydb.core.Flyway$1.execute()

File Flyway.java:918, in org.flywaydb.core.Flyway$1.execute()

File Flyway.java:78, in org.flywaydb.core.Flyway.access$100()

File Flyway.java:1037, in org.flywaydb.core.Flyway.doValidate()

Exception: Java Exception

The above exception was the direct cause of the following exception:

org.flywaydb.core.api.FlywayException     Traceback (most recent call last)
File ~/hostedtoolcache/Python/3.8.18/x64/lib/python3.8/site-packages/ixmp/backend/jdbc.py:297, in JDBCBackend.__init__(self, jvmargs, **kwargs)
    296 try:
--> 297     self.jobj = java.Platform("Python", properties)
    298 except java.NoClassDefFoundError as e:  # pragma: no cover

org.flywaydb.core.api.FlywayException: org.flywaydb.core.api.FlywayException: Validate failed: Detected failed migration to version 1 (hsql base version)

During handling of the above exception, another exception occurred:

RuntimeError                              Traceback (most recent call last)
Cell In[2], line 2
      1 # launch the ix modeling platform using the default local database
----> 2 mp = ixmp.Platform()

File ~/hostedtoolcache/Python/3.8.18/x64/lib/python3.8/site-packages/ixmp/core/platform.py:94, in Platform.__init__(self, name, backend, **backend_args)
     88     raise ValueError(
     89         f"backend class {repr(backend_class_name)} not among "
     90         + str(sorted(BACKENDS.keys()))
     91     )
     93 # Instantiate the backend
---> 94 self._backend = backend_class(**kwargs)

File ~/hostedtoolcache/Python/3.8.18/x64/lib/python3.8/site-packages/ixmp/backend/jdbc.py:320, in JDBCBackend.__init__(self, jvmargs, **kwargs)
    318     else:
    319         _raise_jexception(e)
--> 320     raise RuntimeError(f"{msg}\n(Java: {jclass})")
    322 # Set the log level
    323 self.set_log_level(log_level)

RuntimeError: when initializing database:
(Java: org.flywaydb.core.api.FlywayException)
On: macos-latest-py3.8, macos-latest-py3.10

FAILED ixmp/tests/test_tutorials.py::test_R_transport - nbclient.exceptions.CellExecutionError: An error occurred while executing the following cell:
------------------
# launch the ix modeling platform using a local HSQL database instance
mp <- ixmp$Platform()
------------------


when initializing database:
(Java: org.flywaydb.core.api.FlywayException)Traceback:

1. ixmp$Platform()
2. py_call_impl(callable, call_args$unnamed, call_args$named)
On: macos-latest-py3.8, macos-latest-py3.10

FAILED ixmp/tests/test_tutorials.py::test_R_transport_scenario - nbclient.exceptions.CellExecutionError: An error occurred while executing the following cell:
------------------
# launch the ix modeling platform using the local default database
mp <- ixmp$Platform()
------------------


when initializing database:
(Java: org.flywaydb.core.api.FlywayException)Traceback:

1. ixmp$Platform()
2. py_call_impl(callable, call_args$unnamed, call_args$named)
On: macos-latest-py3.8, macos-latest-py3.10

FAILED ixmp/tests/backend/test_jdbc.py::test_del_ts - assert 8 == (1 + 8)
 +  where 8 = len(<WeakKeyDictionary at 0x120d52330>)
 +    where <WeakKeyDictionary at 0x120d52330> = <ixmp.backend.jdbc.JDBCBackend object at 0x14b0e3890>.jindex
 +      where <ixmp.backend.jdbc.JDBCBackend object at 0x14b0e3890> = <ixmp.core.platform.Platform object at 0x14b0e2bd0>._backend
On: macos-latest-py3.12

FAILED ixmp/tests/core/test_timeseries.py::TestTimeSeries::test_last_update[TimeSeries] - assert datetime.timedelta(seconds=1, microseconds=390684) < datetime.timedelta(seconds=1)
 +  where datetime.timedelta(seconds=1, microseconds=390684) = abs((datetime.datetime(2024, 1, 12, 6, 36, 10, 712000) - datetime.datetime(2024, 1, 12, 6, 36, 12, 102684)))
 +    where datetime.datetime(2024, 1, 12, 6, 36, 12, 102684) = <built-in method now of type object at 0x109bc0ba8>()
 +      where <built-in method now of type object at 0x109bc0ba8> = datetime.now
 +  and   datetime.timedelta(seconds=1) = timedelta(seconds=1)
On: macos-latest-py3.12

FAILED ixmp/tests/core/test_platform.py::test_export_timeseries_data - AssertionError: DataFrame are different

DataFrame shape mismatch
[left]:  (2, 10)
[right]: (0, 10)
On: macos-latest-py3.8, macos-latest-py3.12

FAILED ixmp/tests/backend/test_jdbc.py::test_connect_message - assert "connected to database 'jdbc:hsqldb:mem://ixmptest' (user: ixmp)..." in ''
 +  where '' = CaptureResult(out='', err='').out
On: windows-latest-py3.9, windows-latest-py3.12

FAILED ixmp/tests/backend/test_jdbc.py::test_del_ts - assert 8 == (1 + 8)
 +  where 8 = len(<WeakKeyDictionary at 0x1264df1a0>)
 +    where <WeakKeyDictionary at 0x1264df1a0> = <ixmp.backend.jdbc.JDBCBackend object at 0x151195730>.jindex
 +      where <ixmp.backend.jdbc.JDBCBackend object at 0x151195730> = <ixmp.core.platform.Platform object at 0x1511949e0>._backend
On: macos-latest-py3.12

FAILED ixmp/tests/backend/test_jdbc.py::test_close - AssertionError: assert 'Database connection could not be closed or was already closed' in ''
 +  where '' = CaptureResult(out='', err='').out
On: windows-latest-py3.8

How to review

• Read the diff and note that the CI checks all pass.

PR checklist

• Continuous integration checks all ✅
• [ ] Add or expand tests; coverage checks both ✅ Just updating test config
• [ ] Add, expand, or update documentation. Just updating test config
• [ ] Update release notes. Just updating test config

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e764f63) 98.9% compared to head (46aa2dc) 98.9%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #510   +/-   ##
=====================================
  Coverage   98.9%   98.9%           
=====================================
  Files         44      44           
  Lines       4794    4794           
=====================================
  Hits        4743    4743           
  Misses        51      51           

[khaeru]

Great, thanks! Please open a separate issue to "Address tests that are flaky with pytest-xdist" (linking this and the other PR) so we can remember to address the underlying issue here.