Cleaning up our code
Before we write any tests, we need to ensure that our code is clean. If there is code that is not being used, then it makes little sense to spend time and effort writing tests for it. If we run our to-do Rust application right now, you may notice that we get a list of warnings about unused code.
This is because we switched from storing our to-do items in a JSON file to using a PostgreSQL database. As a result, the code that handled the reading and writing to JSON files became redundant. We can remove this redundant code by deleting the src/processes.rs and src/state.rs files, and removing mod state; and mod processes; lines from the main.rs file.
Once this is done, we then remove all the functionality from all the traits in the src/to_do/structs/traits/{pending.done}.rs directory as the reading and writing of data has been passed onto the database and data model structs. We also have to remove the mod traits; line from the src/to_do/structs/mod.rs file. Now...