avoid pyarrow import error during test collection

Author: jorisvandenbossche

pandas/conftest.py

@@ -1355,11 +1355,9 @@ def object_dtype(request):
 @pytest.fixture(
     params=[
         np.dtype("object"),
-        pd.StringDtype("python"),
-        pytest.param(pd.StringDtype("pyarrow"), marks=td.skip_if_no("pyarrow")),
-        pytest.param(
-            pd.StringDtype("pyarrow", na_value=np.nan), marks=td.skip_if_no("pyarrow")
-        ),
+        ("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")),
     ],
     ids=[
         "string=object",
@@ -1376,7 +1374,13 @@ def any_string_dtype(request):
     * 'string[pyarrow]' (NA variant)
     * 'str' (NaN variant, with pyarrow)
     """
-    return request.param
+    if isinstance(request.param, np.dtype):
+        return request.param
+    else:
+        # need to instantiate the StringDtype here instead of in the params
+        # to avoid importing pyarrow during test collection
+        storage, na_value = request.param
+        return pd.StringDtype(storage, na_value)
 
 
 @pytest.fixture(params=tm.DATETIME64_DTYPES)