set installer.parallel to false for reproducible output

tests/console/commands/test_add.py

@@ -27,6 +27,7 @@
     from pytest_mock import MockerFixture
     from tomlkit import TOMLDocument
 
+    from poetry.config.config import Config
     from poetry.poetry import Poetry
     from poetry.utils.env import MockEnv
     from poetry.utils.env import VirtualEnv
@@ -37,6 +38,13 @@
     from tests.types import ProjectFactory
 
 
+@pytest.fixture(autouse=True)
+def config(config: Config) -> Config:
+    # Disable parallel installs to get reproducible output.
+    config.merge({"installer": {"parallel": False}})
+    return config
+
+
 @pytest.fixture
 def poetry_with_up_to_date_lockfile(
     project_factory: ProjectFactory, fixture_dir: FixtureDirGetter