[Good First Issue] List required of functions to create tests for

Currently, the tests/ directory does not test against every other function to give expected results.

The work towards testing should be done in these phases,

1. List functions that need to have unit tests created
2. Create a mechanism to fetch GeoJSONs from the API that are guaranteed the right results to test against
3. Assert the functionality is working as expected with the fetched data

Help is required with the 1st step. Having a list of unit tests to implement would be great - not everything can be tested.

まず、既存の tests/ ディレクトリと、そこに含まれる Python パッケージの関数を確認します。そのカバレッジを、利用可能な Mapillary API および GeoJSON 関連の機能と比較します。フェーズ 1 では、価値のあるユニットテストの文書化された一覧を作成すれば完了です。API データの取得とアサーションの追加は後のフェーズで行います。