keep the test simple by triggering mutation in the first row and column for frame axis test

Author: ntachukwu

pandas/tests/copy_view/test_methods.py

@@ -247,8 +247,8 @@ def test_set_frame_axis(using_copy_on_write):
         assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
 
     # mutating df2 triggers a copy-on-write for that column / block
-    df2.iloc[0, 1] = 0
-    assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+    df2.iloc[0, 0] = 0
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
     tm.assert_frame_equal(df, df_orig)