tests: Run each test in separate config/cache dirs

Run each CLI command in a separate config/cache dir, to avoid leaks
between tests. Moreover, this way we are able to check the contents of
the config/cache dirs for a single CLI run.

tests/test_cli.py

@@ -10,6 +10,7 @@ import tempfile
 import traceback
 from pathlib import Path
 from typing import Sequence
+from unittest import mock
 
 import pytest
 from click.testing import CliRunner, Result
@@ -129,6 +130,8 @@ class TestCli(TestBase):
         if os.environ.get("DUMMY_CONVERSION", False):
             args = ("--unsafe-dummy-conversion", *args)
 
+        with tempfile.TemporaryDirectory() as t:
+            tmp_dir = Path(t)
             # TODO: Replace this with `contextlib.chdir()` [1], which was added in
             # Python 3.11.
             #
@@ -137,6 +140,11 @@ class TestCli(TestBase):
                 if tmp_path is not None:
                     cwd = os.getcwd()
                     os.chdir(tmp_path)
+
+                with mock.patch(
+                    "dangerzone.isolation_provider.container.get_tmp_dir",
+                    return_value=t,
+                ):
                     result = CliRunner().invoke(cli_main, args)
             finally:
                 if tmp_path is not None: