Ensure exceptions which occur during install are propagated

tests/test_installer.py

@@ -1,11 +1,14 @@
 # pylint: disable=missing-module-docstring, redefined-outer-name, unused-argument, wrong-import-order, unused-import
 import time
+from unittest import mock
 
+import pytest
 import tox.venv
 from poetry.factory import Factory
 
 from .fixtures import mock_poetry_factory
 from .fixtures import mock_venv
+from tox_poetry_installer import _poetry
 from tox_poetry_installer import installer
 from tox_poetry_installer import utilities
 
@@ -57,3 +60,28 @@ def test_parallelization(mock_venv, mock_poetry_factory):
     assert round(parallel * 5) == round(sequential)
     assert round(sequential) == len(set(to_install))
     assert round(parallel * 5) == len(set(to_install))
+
+
+@pytest.mark.parametrize("num_threads", (0, 8))
+def test_propagates_exceptions_during_installation(
+    mock_venv, mock_poetry_factory, num_threads
+):
+    # Assert that an exception which occurs during installation is properly raised.
+    # Regression test for https://github.com/enpaul/tox-poetry-installer/issues/86
+    poetry = Factory().create_poetry(None)
+    packages: utilities.PackageMap = {
+        item.name: item for item in poetry.locker.locked_repository().packages
+    }
+    to_install = [packages["toml"]]
+    venv = tox.venv.VirtualEnv()
+    fake_exception = ValueError("my testing exception")
+
+    with mock.patch.object(
+        _poetry,
+        "PipInstaller",
+        **{"return_value.install.side_effect": fake_exception},
+    ):
+        with pytest.raises(ValueError) as exc_info:
+            installer.install(poetry, venv, to_install, num_threads)
+
+    assert exc_info.value is fake_exception