test: x/mint thirdening - identify rounding errors

[p0mvn]

Part of: #1839

What is the purpose of the change

There have been concerns about minting rounding errors that were causing total osmo supply to be slightly off.

This change root causes some of the rounding issues related to total supply. The newly introduced test identifies the 2 sources:

1. Epoch provisions truncation
2. Developer rewards truncation

The test works by running AfterEpochEnd hook 366 times (until and including thirdening). Before the 366th AfterEpochEnd, we make an assertion on the total supply.

If the aforementioned assertion was to be made directly against the actual osmo supply value, it would be off by 2619.999999999999999705. Instead, we accumulate the delta from the two rounding error sources and add them to the actual supply value to make the assertion pass:

// 299_999_999_999_999.999999999999999705 == 299_999_999_997_380 + 2555 + 64.999999999999999705
require.Equal(t, expectedTotalProvisionedSupply, actualTotalProvisionedSupply.Add(devRewardsDelta).Add(epochProvisionsDelta))

• Note that the setup excludes the 100M initial mainnet supply and only includes the minted per-epoch provisions.

Essentially, this test helps to root cause the rounding errors. We should refactor and fix the rounding errors. Then, the test should potentially be removed.

Testing and Verifying

go test -timeout 30s -run ^TestAfterEpochEnd_FirstYearThirdening_RealParameters$ github.com/osmosis-labs/osmosis/v7/x/mint/keeper

Documentation and Release Note

• Does this pull request introduce a new feature or user-facing behavior changes? no
• Is a relevant changelog entry added to the Unreleased section in CHANGELOG.md? no
• How is the feature or change documented? not applicable