some tests and major cleanup

pkg/store/store.go

@@ -2,16 +2,12 @@
 
 package store
 
-import "fmt"
-
-func storeErr(i interface{}) error {
-	return fmt.Errorf("store: %s", i)
-}
+import "errors"
 
 var (
-	ErrKeyNotFound = storeErr("key not found")
-	ErrWriterIsNil = storeErr("writer is nil")
-	ErrReaderIsNil = storeErr("reader is nil")
+	ErrKeyNotFound = errors.New("store: key not found")
+	ErrWriterIsNil = errors.New("store: writer is nil")
+	ErrReaderIsNil = errors.New("store: reader is nil")
 )
 
 type Store interface {