/starknet-lagos-con-workshop

This repo is home to fundamentals required to get started with testing your Starknet contracts using snforge

Primary LanguageCairo

Starknet Lagos Conference Hands-on Testing Workshop

Introduction to Testing Using snforge

Important Cheat Codes

prank - changes the caller address for contracts, for a number of calls. Calling a cheatcode with CheatSpan::TargetCalls(N) is going to activate the cheatcode for N calls to a specified CheatTarget, after which it's going to be automatically canceled. Of course the cheatcode can still be canceled before its CheatSpan goes down to 0 - simply call stop_prank on the target manually.

prank(CheatTarget::One(contract_address), new_caller_address, CheatSpan::TargetCalls(1))

start_prank - changes the caller address for contracts

    // Change the caller address to user_1 before calling increase_count
    start_prank(CheatTarget::One(contract_address), user_1_addr);

stop_prank - cancels the prank / start_prank for contracts

// The address when calling contract at the `contract_address` address will no longer be changed
stop_prank(CheatTarget::One(contract_address));

Error Handling

Some tests are expected fail. This is useful when you want to verify that an action fails as expected. The following methodologies can be deployed:

  1. Using #[should_panic(expected: ('panic message', ))] attribute

  2. Using SafeDispatcher, we can test that the function in fact panics with an expected message. To utilize SafeDispatcher, it's required to annotate its usage with #[feature("safe_dispatcher")]

Events

Asserting events manually

  • After contract deployment we created the spy with spy_events cheatcode. From this moment all events emitted by the SpyEventsChecker contract will be spied.
  • We have to call fetch_events method on the created spy to load emitted events into it.
  • When events are fetched they are loaded into the events property of our spy, and we can assert them.
  • If the event is emitted by calling self.emit method, its hashed name is saved under the keys.at(0) (this way Starknet handles events)
  • It is worth noting that when we call the method which emits an event, spy is not updated immediately.

Asserting emission with assert_emitted method

  • After the contract is called, we don't have to call fetch_events on the spy (it is done inside the assert_emitted method).
  • assert_emitted takes the array snapshot of tuples (ContractAddress, event) we expect were emitted.
  • After the assertion, found events are removed from the spy. It stays clean and ready for the next events.