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_artist_repo.go

@@ -0,0 +1,47 @@
+package persistence
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+
+	"github.com/deluan/gosonic/domain"
+)
+
+func CreateMockArtistRepo() *MockArtist {
+	return &MockArtist{}
+}
+
+type MockArtist struct {
+	domain.ArtistRepository
+	data map[string]*domain.Artist
+	err  bool
+}
+
+func (m *MockArtist) SetError(err bool) {
+	m.err = err
+}
+
+func (m *MockArtist) SetData(j string, size int) {
+	m.data = make(map[string]*domain.Artist)
+	var l = make([]domain.Artist, size)
+	err := json.Unmarshal([]byte(j), &l)
+	if err != nil {
+		fmt.Println("ERROR: ", err)
+	}
+	for _, a := range l {
+		m.data[a.Id] = &a
+	}
+}
+
+func (m *MockArtist) Exists(id string) (bool, error) {
+	_, found := m.data[id]
+	return found, nil
+}
+
+func (m *MockArtist) Get(id string) (*domain.Artist, error) {
+	if m.err {
+		return nil, errors.New("Error!")
+	}
+	return m.data[id], nil
+}