Unify the store tests (#1952)

Add more tests for store

store/memory/memory.go

@@ -136,13 +136,19 @@ func (m *memoryStore) list(prefix string, limit, offset uint) []string {
 
 	if limit != 0 || offset != 0 {
 		sort.Slice(allKeys, func(i, j int) bool { return allKeys[i] < allKeys[j] })
-		min := func(i, j uint) uint {
-			if i < j {
-				return i
+		sort.Slice(allKeys, func(i, j int) bool { return allKeys[i] < allKeys[j] })
+		end := len(allKeys)
+		if limit > 0 {
+			calcLimit := int(offset + limit)
+			if calcLimit < end {
+				end = calcLimit
 			}
-			return j
 		}
-		return allKeys[offset:min(limit, uint(len(allKeys)))]
+
+		if int(offset) >= end {
+			return nil
+		}
+		return allKeys[offset:end]
 	}
 
 	return allKeys