diff --git a/tests/utils/test_helpers.py b/tests/utils/test_helpers.py
index 010637c693f..5e54cc91674 100644
--- a/tests/utils/test_helpers.py
+++ b/tests/utils/test_helpers.py
@@ -19,11 +19,13 @@
 from poetry.utils._compat import WINDOWS
 from poetry.utils.helpers import Downloader
 from poetry.utils.helpers import HTTPRangeRequestSupportedError
+from poetry.utils.helpers import directory
 from poetry.utils.helpers import download_file
 from poetry.utils.helpers import ensure_path
 from poetry.utils.helpers import extractall
 from poetry.utils.helpers import get_file_hash
 from poetry.utils.helpers import get_highest_priority_hash_type
+from poetry.utils.helpers import merge_dicts
 
 
 if TYPE_CHECKING:
@@ -157,6 +159,20 @@ def test_download_file(
     assert http.calls[-1].request.headers["Accept-Encoding"] == "Identity"
 
 
+def test_downloader_with_invalid_content_length(
+    http: responses.RequestsMock, tmp_path: Path
+) -> None:
+    url = "https://foo.com/demo.txt"
+    http.get(url, body=b"demo", headers={"Content-Length": "invalid"})
+    dest = tmp_path / "demo.txt"
+
+    downloader = Downloader(url, dest)
+
+    assert downloader.total_size == 0
+    assert list(downloader.download_with_progress(chunk_size=2)) == [2, 4]
+    assert dest.read_bytes() == b"demo"
+
+
 def test_download_file_recover_from_error(
     http: responses.RequestsMock, fixture_dir: FixtureDirGetter, tmp_path: Path
 ) -> None:
@@ -348,6 +364,37 @@ def test_ensure_path_directory(tmp_path: Path) -> None:
     assert ensure_path(path=path, is_directory=True) is path
 
 
+def test_directory_restores_working_directory_after_error(tmp_path: Path) -> None:
+    cwd = Path.cwd()
+
+    with pytest.raises(RuntimeError), directory(tmp_path):
+        assert Path.cwd() == tmp_path
+        raise RuntimeError("expected failure")
+
+    assert Path.cwd() == cwd
+
+
+def test_merge_dicts_merges_nested_mappings() -> None:
+    config = {
+        "installer": {"parallel": True, "max-workers": 4},
+        "virtualenvs": {"create": True},
+    }
+
+    merge_dicts(
+        config,
+        {
+            "installer": {"max-workers": 8},
+            "repositories": {"foo": {"url": "https://foo.example/simple/"}},
+        },
+    )
+
+    assert config == {
+        "installer": {"parallel": True, "max-workers": 8},
+        "virtualenvs": {"create": True},
+        "repositories": {"foo": {"url": "https://foo.example/simple/"}},
+    }
+
+
 @pytest.mark.parametrize("relative", [False, True])
 @pytest.mark.parametrize("existing", [False, True])
 def test_extractall_sdist_no_path_traversal(