Tests for submission service

[kolyaopahle]

Checklist

• Test your changes as thoroughly as possible before you commit them. Preferably, automate your test by unit/integration tests.
• If this PR comes from a fork, please Allow edits from maintainers
• Set a speaking title. Format: {task_name} (closes #{issue_number}). For example: Use logger (closes # 41)
• Link your Pull Request to an issue (if applicable)
• Create Work In Progress [WIP] pull requests only if you need clarification or an explicit review before you can continue your work item.
• Make sure that your PR is not introducing unnecessary reformatting (e.g., introduced by on-save hooks in your IDE)
• Make sure that your PR does not contain changes in strings.xml (see issue Text and Translation Contributions #72)
• Make sure that your PR does not contain compiled sources (already set by the default .gitignore) and / or binary files

Description

This PR introduces some new tests for the SubmissionService test suite