Update test_deprecated_kwargs.py

Minimize code executed within assert_produces_warning context.

Author: alexitkes

pandas/tests/io/json/test_deprecated_kwargs.py

@@ -15,12 +15,15 @@ def test_deprecated_kwargs():
     argument passed as positional.
     """
     df = pd.DataFrame({"A": [2, 4, 6], "B": [3, 6, 9]}, index=[0, 1, 2])
+    buf = df.to_json(orient="split")
     with tm.assert_produces_warning(FutureWarning):
-        assert_frame_equal(df, read_json(df.to_json(orient="split"), "split"))
+        assert_frame_equal(df, read_json(buf, "split"))
+    buf = df.to_json(orient="columns")
     with tm.assert_produces_warning(FutureWarning):
-        assert_frame_equal(df, read_json(df.to_json(orient="columns"), "columns"))
+        assert_frame_equal(df, read_json(buf, "columns"))
+    buf = df.to_json(orient="index")
     with tm.assert_produces_warning(FutureWarning):
-        assert_frame_equal(df, read_json(df.to_json(orient="index"), "index"))
+        assert_frame_equal(df, read_json(buf, "index"))
 
 
 def test_good_kwargs():