Enhance the FPI tests.

[Fumuran]

What should be done?

See #896 (comment)

How should it be done?

Create new tests which will test the required capabilities.

When is this task done?

The task is done when the tests will also check the correctness of the foreign procedure invocation from within another account as a part of a complete transaction.

Additional context

No response

[Fumuran]

Currently we have these FPI tests:

• "Memory" test, which checks the memory layout of the foreign account. It has three subtests which check:
  • Obtaining the storage item (checks the item value)
  • Obtaining the storage map item (checks the item value)
  • Obtaining the storage item twice (checks that we reused the account data which was loaded during the first item obtaining, asserting that the next account slot was uninitialized).
• "Integration" test, which gets the storage item and storage map item, checking their correctness. As opposed to the "memory" test, it uses TransactionExecutor instead of TransactionContext to execute the transaction script.

I think the basic capabilities of obtaining values and map values are tested, the only thing I can imagine is to make sure that the script that checks whether this foreign account was already loaded is working correctly by creating more complex test and using several different accounts (for now we used only one). But it should be fine too, since we check the basic case in the "memory" test.

cc @bobbinth

[bobbinth]

I would add a test which used two different accounts. The test could work like so:

• Make a call to account 1 - e.g., read storage value.
• Make a call to account 2 - e.g., read storage value.
• Make a call to account 1 again - e.g., read storage value.

This way we can check that handling of multiple accounts works correctly (and that we don't load account 1 twice for some reason).