Put sumo:find_one/2 function back.

General fixes according with PR comments.

src/adapter_test_helpers/sumo_basic_test_helper.erl

@@ -32,7 +32,7 @@ find(Config) ->
   Module = sumo_config:get_prop_value(Name, module),
 
   [First, Second | _] = sumo:find_all(Name),
-  First = sumo:fetch(Name, Module:id(First)),
+  First = sumo:find_one(Name, [{id, Module:id(First)}]),
   Second = sumo:fetch(Name, Module:id(Second)),
   notfound = sumo:fetch(Name, 0),
   ok.

src/sumo.erl

@@ -39,6 +39,7 @@
 -export([
   persist/2,
   fetch/2,
+  find_one/2,
   find_all/1, find_all/4,
   find_by/2, find_by/4, find_by/5,
   delete/2,
@@ -133,6 +134,14 @@ fetch(DocName, Id) ->
     {error, Reason} -> Reason
   end.
 
+%% @doc Returns 1 doc that matches the given Conditions.
+-spec find_one(schema_name(), conditions()) -> user_doc() | notfound.
+find_one(DocName, Conditions) ->
+  case find_by(DocName, Conditions, 1, 0) of
+    []          -> notfound;
+    [First | _] -> First
+  end.
+
 %% @doc Returns all docs from the given store.
 -spec find_all(schema_name()) -> [user_doc()].
 find_all(DocName) ->
@@ -313,5 +322,4 @@ normalize_sort_fields(SortFields) when is_list(SortFields) ->
 
 %% @private
 get_docs() ->
-  {ok, Docs} = application:get_env(sumo_db, docs),
-  Docs.
+  application:get_env(sumo_db, docs, []).