Add getter generation macro for test purposes

[theochap]

Description

When testing data structures, we often need to generate public getters to get (normally) private elements of data structures. This issue offers to add a macro that would automatically generate getters for test configuration for the data structures where it is applied.

Example

For the data structure SlotCommit:

pub struct SlotCommit<S: SlotData, B, T> {
    slot_data: S,
    batch_receipts: Vec<BatchReceipt<B, T>>,
    num_txs: usize,
    num_events: usize,
}

The macro would generate

#[cfg(test)]
impl<S: SlotData, B, T> SlotCommit<S, B, T> {
    pub fn slot_data(&self) -> &S {
        &self.slot_data
    }

    pub fn batch_receipts(&self) -> &Vec<BatchReceipt<B, T>> {
        &self.batch_receipts
    }

    pub fn num_txs(&self) -> &usize {
        &self.num_txs
    }

    pub fn num_events(&self) -> &usize {
        &self.num_events
    }
}

[theochap]

I can take this issue if people think that's useful enough!

[citizen-stig]

I think it can be a good idea. @theochap , could you give one or several concrete examples where it would be useful? I am asking, because this solution might bring some burden on test maintenance, because changin private methods can potentially break the tests. Usually it is a good question to ask, why test require access to private fields? If it is black-box testing, then it should be possible to check correctness using public methods. Maybe design of public methods require adjustments?

[citizen-stig]

Also, this only work inside crate, because even in test, other crates are not compiled for testing. Then it means that pub(crate) might be useful to have

[neysofu]

I think practical uses for such macro would be limited and there's several 3rd-party crates that do this already; we could use any of those if this ever becomes necessary. I propose closing this issue.