add test to verify lock is changed on install failure

tests/console/commands/test_add.py

@@ -32,16 +32,25 @@
 
 @pytest.fixture
 def poetry_with_up_to_date_lockfile(
-    project_factory: ProjectFactory, fixture_dir: FixtureDirGetter
+    project_factory: ProjectFactory,
+    fixture_dir: FixtureDirGetter,
+    repo: TestRepository,
+    command_tester_factory: CommandTesterFactory,
 ) -> Poetry:
     source = fixture_dir("up_to_date_lock")
 
-    return project_factory(
+    poetry = project_factory(
         name="foobar",
         pyproject_content=(source / "pyproject.toml").read_text(encoding="utf-8"),
         poetry_lock_content=(source / "poetry.lock").read_text(encoding="utf-8"),
     )
 
+    # ensure poetry.lock with updated syntax
+    repo.add_package(get_package("docker", "4.3.1"))
+    command_tester_factory("lock", poetry=poetry).execute()
+
+    return poetry
+
 
 @pytest.fixture()
 def tester(command_tester_factory: CommandTesterFactory) -> CommandTester:
@@ -2199,3 +2208,23 @@ def test_add_with_dry_run_keep_files_intact(
     assert (
         poetry_with_up_to_date_lockfile._locker.lock_data == original_lockfile_content
     )
+
+
+def test_add_should_not_change_lock_file_when_dependency_installation_fail(
+    poetry_with_up_to_date_lockfile: Poetry,
+    repo: TestRepository,
+    command_tester_factory: CommandTesterFactory,
+    mocker: MockerFixture,
+):
+    tester = command_tester_factory("add", poetry=poetry_with_up_to_date_lockfile)
+
+    repo.add_package(get_package("cachy", "0.2.0"))
+
+    original_pyproject_content = poetry_with_up_to_date_lockfile.file.read()
+    original_lockfile_content = poetry_with_up_to_date_lockfile.locker.lock_data
+
+    mocker.patch("poetry.installation.installer.Installer._execute", return_value=1)
+    tester.execute("cachy")
+
+    assert poetry_with_up_to_date_lockfile.file.read() == original_pyproject_content
+    assert poetry_with_up_to_date_lockfile.locker.lock_data == original_lockfile_content