diff --git a/pyproject.toml b/pyproject.toml
index 89f47c66..ceb13694 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -39,6 +39,7 @@ authors = [{ name = "Owkin, Inc." }]
 [project.optional-dependencies]
 dev = [
     "pandas",
+    "numpy",
     "pytest",
     "pytest-cov",
     "pytest-mock",
diff --git a/tests/tools/test_opener.py b/tests/tools/test_opener.py
index 6d37343b..58e88697 100644
--- a/tests/tools/test_opener.py
+++ b/tests/tools/test_opener.py
@@ -11,26 +11,26 @@
 from substratools.workspace import DEFAULT_INPUT_DATA_FOLDER_PATH
 
 
-# @pytest.fixture
-# def tmp_cwd(tmp_path):
-#     # create a temporary current working directory
-#     new_dir = tmp_path / "workspace"
-#     new_dir.mkdir()
+@pytest.fixture
+def tmp_cwd(tmp_path):
+    # create a temporary current working directory
+    new_dir = tmp_path / "workspace"
+    new_dir.mkdir()
 
-#     old_dir = os.getcwd()
-#     os.chdir(new_dir)
+    old_dir = os.getcwd()
+    os.chdir(new_dir)
 
-#     yield new_dir
+    yield new_dir
 
-#     os.chdir(old_dir)
+    os.chdir(old_dir)
 
 
-def test_load_opener_not_found():
+def test_load_opener_not_found(tmp_cwd):
     with pytest.raises(ImportError):
         load_from_module()
 
 
-def test_load_invalid_opener():
+def test_load_invalid_opener(tmp_cwd):
     invalid_script = """
 def get_data():
     raise NotImplementedError
@@ -42,7 +42,7 @@ def get_data():
         load_from_module()
 
 
-def test_load_opener_as_class():
+def test_load_opener_as_class(tmp_cwd):
     script = """
 from substratools import Opener
 class MyOpener(Opener):
@@ -58,7 +58,7 @@ def fake_data(self, n_samples):
     assert o.get_data() == "data_class"
 
 
-def test_load_opener_from_path(valid_opener_code):
+def test_load_opener_from_path(tmp_cwd, valid_opener_code):
     dirpath = tmp_cwd / "myopener"
     dirpath.mkdir()
     path = dirpath / "my_opener.py"
@@ -74,7 +74,7 @@ def test_load_opener_from_path(valid_opener_code):
     assert o.get_data()[0] == "X"
 
 
-def test_opener_check_folders():
+def test_opener_check_folders(tmp_cwd):
     script = """
 from substratools import Opener
 class MyOpener(Opener):