changed the tests so that it downloads testing files if not present
changed the tests so that it downloads testing files if not present


Former-commit-id: e6fce61bf1541f50945ac662d987e7654ff74753
Former-commit-id: db18120cf586a7ee783e8adbefe3acfa68977052
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox