TST (string dtype): replace string_storage fixture with explicit storage/na_value keyword arguments for dtype creation

pandas/conftest.py

@@ -1310,6 +1310,24 @@ def string_storage(request):
     return request.param
 
 
+@pytest.fixture(
+    params=[
+        ("python", pd.NA),
+        pytest.param(("pyarrow", pd.NA), marks=td.skip_if_no("pyarrow")),
+        pytest.param(("pyarrow", np.nan), marks=td.skip_if_no("pyarrow")),
+    ]
+)
+def string_dtype_arguments(request):
+    """
+    Parametrized fixture for StringDtype storage and na_value.
+
+    * 'python' + pd.NA
+    * 'pyarrow' + pd.NA
+    * 'pyarrow' + np.nan
+    """
+    return request.param
+
+
 @pytest.fixture(
     params=[
         "numpy_nullable",

pandas/tests/arrays/string_/test_string.py

@@ -23,9 +23,10 @@
 
 
 @pytest.fixture
-def dtype(string_storage):
-    """Fixture giving StringDtype from parametrized 'string_storage'"""
-    return pd.StringDtype(storage=string_storage)
+def dtype(string_dtype_arguments):
+    """Fixture giving StringDtype from parametrized storage and na_value arguments"""
+    storage, na_value = string_dtype_arguments
+    return pd.StringDtype(storage=storage, na_value=na_value)
 
 
 @pytest.fixture

pandas/tests/extension/test_string.py

@@ -59,8 +59,9 @@ def chunked(request):
 
 
 @pytest.fixture
-def dtype(string_storage):
-    return StringDtype(storage=string_storage)
+def dtype(string_dtype_arguments):
+    storage, na_value = string_dtype_arguments
+    return StringDtype(storage=storage, na_value=na_value)
 
 
 @pytest.fixture