[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.

首先检查现有的 tests/ 目录以及其中覆盖的 Python 包函数。将该覆盖范围与可用的 Mapillary API 和 GeoJSON 相关功能进行比较。完成标准是为第 1 阶段编写一份有文档记录的、值得实现的单元测试列表；获取 API 数据和添加断言属于后续阶段。