Smart Contracts: Contract.call_function/3 mockable

[bchamagne]

Description

We need to be able to mock it in the playground

Type of change

• Refactor

How Has This Been Tested?

Manual test via playground

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules