Template: Add types/genesis_test.go

[lumtis]

Is your feature request related to a problem? Please describe.
The TestGenesisState_Validate tests from types/genesis_test.go are extremely important when creating a blockchain because Validate is the method that prevents the blockchain starting from an inconsistent state.

Describe the solution you'd like
We should automatically generate a types/genesis_test.go that contains a template for those tests and facilitate the developer the implementation of them.
We can also add new checks when scaffolding types (check that no duplicated IDs can be provided)

[ilgooz]

For the Validate funcs, I saw some repetitive logic in spn like checking duplicated items in slices. I propose to create a validator helper pkg in tendermint/spm to make it easy to validate some common things.

For this spesific case with slices, we can implement something like:

// CheckDuplicated returns isDuplicated=false if all of the itr returns with the same type but with a different value.
// when there is a duplicated item, duplicatedItem is not nil and equals to the first found duplicated item.
// itr called for each item.
validation.CheckDuplicated(items interface{}, itr func(item interface{}) (value interface{})) (isDuplicated bool, duplicatedItem interface{})


validation.CheckDuplicated(coordinators, func(item interface{}) interface{} {
    return item.(Coordinator).Address
}) 

For max. ids:

// CheckOK returns isAllOK=true if all of the itr returns with true.
// when there is a non ok item, firstNonOK is not nil and equals to the first found non ok item.
validation.CheckOK(items interface{}, itr func(item interface{}) (ok bool)) (isAllOK bool, firstNonOK interface{})

validation.CheckOK(coordinators, func(item interface{}) (ok bool) {
    return item.(Coordinator).CoordinatorId >= count
}) 

[lumtis]

That's nice to avoid duplicated generated code as much as possible. Although we must also keep in mind that we scaffold code that is eventually aimed to be modified and customized afterward

For example, in the case of spn genesis, we check that there is no duplicated chain ID with a map inside a loop, but then we reuse the same map to check that a request is always associated with an existing chain ID. Also, by having a loop for every lists of the genesis, we provide a template that allows the develop to easily add custom logic for each types in the genesis

Finally, if we need to factorize code, I would be more confortable with generating the helpers in the chain source, so the developer keeps full control over the scaffolded code