Introduced engine.Scrobbler

Also refactored mocks into their original packages, to avoid cyclic references. Is there a better way to have mocks in GoLang tests?

persistence/mock_index_repo.go

@@ -0,0 +1,38 @@
+package persistence
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+
+	"github.com/deluan/gosonic/domain"
+)
+
+func CreateMockArtistIndexRepo() *MockArtistIndex {
+	return &MockArtistIndex{}
+}
+
+type MockArtistIndex struct {
+	domain.ArtistIndexRepository
+	data domain.ArtistIndexes
+	err  bool
+}
+
+func (m *MockArtistIndex) SetError(err bool) {
+	m.err = err
+}
+
+func (m *MockArtistIndex) SetData(j string, length int) {
+	m.data = make(domain.ArtistIndexes, length)
+	err := json.Unmarshal([]byte(j), &m.data)
+	if err != nil {
+		fmt.Println("ERROR: ", err)
+	}
+}
+
+func (m *MockArtistIndex) GetAll() (*domain.ArtistIndexes, error) {
+	if m.err {
+		return nil, errors.New("Error!")
+	}
+	return &m.data, nil
+}