feat: add test case covering recursive functions

[vitorpy]

Closes #303

• I have updated CHANGELOG.md
• I have added tests to demonstrate the contribution is correctly implemented: this usually includes both positive and negative tests, showing the happy path(s) and featuring intentionally broken cases
• I have run all the tests locally and no test failure was reported
• I did not do unrelated and/or undiscussed refactorings

[Gusarich]

let's also add a recursive function outside of the contract (not a get-method) and call it in a separate function

[Gusarich]

LGTM

[anton-trunov]

LGTM too, just a nitpick in the changelog