How to mock in tests?

[lumos42]

Hi, Is there a way to mock function calls to write unit tests?

Let's say module A calls module B, and I want to test module A only. Is there a way to mock calls to module B such that tests can be isolated?

[0xbrw]

You can look through this code example, module A would be aptogotchi.move and module B would be food.move:
https://github.com/aptos-labs/aptogotchi-intermediate/blob/main/move/sources/aptogotchi.move

As for mocking you can create a #test_only function to help perform your mock.

[0xbrw]

Another option is in your Move.toml file you can specify module B as a [dev-dependencies] and mock the desired function in module B. Just be sure to run test with the --dev flag. For example, aptos move test --dev

[lumos42]

Perhaps I didn't explain my question well. I'm looking to mock function calls, so in your example, let's say I wanted to test the aptogotchi::feed function, but the function calls food::burn_food. Now my unit tests for aptogotchi::feed should not depend on other modules, so is there a way to mock calls to food::burn_food such that while testing it doesn't make an actual call to food package but uses the mock response provided by me? This is a common functionality provided in languages for ease of testing.

More details here.

The way to do it in Solidity is to have an interface IFood and have an implementation for a real food module and one for mock food. And then for test setup we can just configure the aptogotchi contract to use mock food.

[0xbrw]

Aptos does not have that mocking functionality yet. For now if you don't want to make a call into module B, I would create a test only helper function.