DOC: Add the description of SparseArray.all

Author: Licht-T

pandas/core/sparse/array.py

@@ -615,6 +615,13 @@ def fillna(self, value, downcast=None):
                                 fill_value=fill_value)
 
     def all(self, axis=0, *args, **kwargs):
+        """
+        Tests whether all elements evaluate True
+
+        Returns
+        -------
+        all : bool
+        """
         nv.validate_all(args, kwargs)
 
         values = self.sp_values