Refactored test utils in VK module

internal/vk/test_cache.go

@@ -0,0 +1,19 @@
+package vk
+
+import "errors"
+
+type testCache struct {
+	table map[string]string
+}
+
+func (t *testCache) Get(cardName string) (string, error) {
+	msg, ok := t.table[cardName]
+	if !ok {
+		return "", errors.New("test")
+	}
+	return msg, nil
+}
+
+func (t *testCache) Set(cardName string, message string) {
+	t.table[cardName] = message
+}