Add `MoveHarness` support

[l-monninger]

Summary

movement-network/movement#1214 uses the MoveHarness to write its tests. Many of these tests will be rewritten in this repository, thus providing the ability to get MoveHarness from *Migrator structs simplifies the addition of said tests.

A MoveHarness can be constructed from a FakeExecutor which can be instantiated at a snapshot with a FakeDataStore.

Warning

FakeDataStore does not seem to have a direct from DB constructor. This is likely because you should not attempt to load all state keys and values into memory—hence the complexity of the loader adapter.

Setting the relevant state keys by iterating over and filtering the total GlobalStorageKey set may be reasonable for some initial checks. But, it’s hard to reason about soundness and completeness.

Note

Because of the warning above and general testing principles, we will still likely want to validate some of the true e2e behavior of the node, not just the behavior within harness for sanity.

[sebtomba]

This is only useful if we can write checks (tests) on the migrated data. It's not evident if this is possible with the FakeDataStore. On the other hand, we should validate the actual end-to-end (e2e) behavior of the node, rather than relying on some fake components. Let's keep the MoveHarness solution as a last resort.

[l-monninger]

This is only useful if we can write checks (tests) on the migrated data. It's not evident if this is possible with the FakeDataStore. On the other hand, we should validate the actual end-to-end (e2e) behavior of the node, rather than relying on some fake components. Let's keep the MoveHarness solution as a last resort.

@sebtomba

I generally agree. I will note, however, that I can populate FakeDataStore. What I can't do is populate it with the entirety of global storage. So, if we determined an appropriate subset of global storage, we could use this for some checks.

At the same time, however, we will ultimately need to check some hitherto undefined properties e2e. So, some parts of this point are moot.