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?

engine/mock_property_repo.go

@@ -0,0 +1,44 @@
+package engine
+
+import (
+	"errors"
+)
+
+func CreateMockPropertyRepo() *MockProperty {
+	return &MockProperty{data: make(map[string]string)}
+}
+
+type MockProperty struct {
+	PropertyRepository
+	data map[string]string
+	err  bool
+}
+
+func (m *MockProperty) SetError(err bool) {
+	m.err = err
+}
+
+func (m *MockProperty) Put(id string, value string) error {
+	if m.err {
+		return errors.New("Error!")
+	}
+	m.data[id] = value
+	return nil
+}
+
+func (m *MockProperty) Get(id string) (string, error) {
+	if m.err {
+		return "", errors.New("Error!")
+	}
+	return m.data[id], nil
+}
+
+func (m *MockProperty) DefaultGet(id string, defaultValue string) (string, error) {
+	v, err := m.Get(id)
+
+	if v == "" {
+		v = defaultValue
+	}
+
+	return v, err
+}