Added mock database request service

internal/usecases/request/mock/mockrequest.go

+package mockrequest
+
+import (
+	"errors"
+	"query-service/internal/entity"
+)
+
+// A Service implements the request usecases (mock)
+type Service struct {
+	throwError bool
+}
+
+// NewService creates a new service (mock)
+func NewService() *Service {
+	return &Service{
+		throwError: false,
+	}
+}
+
+// SendAQLQuery sends the query to arangoDB and parses the result (mock)
+func (s *Service) SendAQLQuery(query string) (*map[string][]entity.Document, error) {
+	mockResult := make(map[string][]entity.Document)
+
+	if !s.throwError {
+		return &mockResult, nil
+	}
+	return nil, errors.New("Database error")
+}
+
+// ToggleError decides whether the convert function throws an error
+func (s *Service) ToggleError() {
+	s.throwError = !s.throwError
+}