Generate Tests Skill

Overview

This skill generates comprehensive test suites for Move contracts with 100% line coverage requirement. Tests verify:

✅ Happy paths (functionality works)
✅ Access control (unauthorized users blocked)
✅ Input validation (invalid inputs rejected)
✅ Edge cases (boundaries, limits, empty states)

Critical Rule: NEVER deploy without 100% test coverage.

Core Workflow

Step 1: Create Test Module

#[test_only]
module my_addr::my_module_tests {
    use my_addr::my_module::{Self, MyObject};
    use aptos_framework::object::{Self, Object};
    use std::string;
    use std::signer;

    // Test constants
    const ADMIN_ADDR: address = @0x100;
    const USER_ADDR: address = @0x200;
    const ATTACKER_ADDR: address = @0x300;

    // ========== Setup Helpers ==========
    // (Reusable setup functions)

    // ========== Happy Path Tests ==========
    // (Basic functionality)

    // ========== Access Control Tests ==========
    // (Unauthorized access blocked)

    // ========== Input Validation Tests ==========
    // (Invalid inputs rejected)

    // ========== Edge Case Tests ==========
    // (Boundaries and limits)
}

Step 2: Write Happy Path Tests

Test basic functionality works correctly:

#[test(creator = @0x1)]
public fun test_create_object_succeeds(creator: &signer) {
    // Execute
    let obj = my_module::create_my_object(
        creator,
        string::utf8(b"Test Object")
    );

    // Verify
    assert!(object::owner(obj) == signer::address_of(creator), 0);
}

#[test(owner = @0x1)]
public fun test_update_object_succeeds(owner: &signer) {
    // Setup
    let obj = my_module::create_my_object(owner, string::utf8(b"Old Name"));

    // Execute
    let new_name = string::utf8(b"New Name");
    my_module::update_object(owner, obj, new_name);

    // Verify (if you have view functions)
    // assert!(my_module::get_object_name(obj) == new_name, 0);
}

#[test(owner = @0x1, recipient = @0x2)]
public fun test_transfer_object_succeeds(
    owner: &signer,
    recipient: &signer
) {
    let recipient_addr = signer::address_of(recipient);

    // Setup
    let obj = my_module::create_my_object(owner, string::utf8(b"Object"));
    assert!(object::owner(obj) == signer::address_of(owner), 0);

    // Execute
    my_module::transfer_object(owner, obj, recipient_addr);

    // Verify
    assert!(object::owner(obj) == recipient_addr, 1);
}

Step 3: Write Access Control Tests

Test unauthorized access is blocked:

#[test(owner = @0x1, attacker = @0x2)]
#[expected_failure(abort_code = my_module::E_NOT_OWNER)]
public fun test_non_owner_cannot_update(
    owner: &signer,
    attacker: &signer
) {
    let obj = my_module::create_my_object(owner, string::utf8(b"Object"));

    // Attacker tries to update (should abort)
    my_module::update_object(attacker, obj, string::utf8(b"Hacked"));
}

#[test(owner = @0x1, attacker = @0x2)]
#[expected_failure(abort_code = my_module::E_NOT_OWNER)]
public fun test_non_owner_cannot_transfer(
    owner: &signer,
    attacker: &signer
) {
    let obj = my_module::create_my_object(owner, string::utf8(b"Object"));

    // Attacker tries to transfer (should abort)
    my_module::transfer_object(attacker, obj, @0x3);
}

#[test(admin = @0x1, user = @0x2)]
#[expected_failure(abort_code = my_module::E_NOT_ADMIN)]
public fun test_non_admin_cannot_configure(
    admin: &signer,
    user: &signer
) {
    my_module::init_module(admin);

    // Regular user tries admin function (should abort)
    my_module::update_config(user, 100);
}

Step 4: Write Input Validation Tests

Test invalid inputs are rejected:

#[test(user = @0x1)]
#[expected_failure(abort_code = my_module::E_ZERO_AMOUNT)]
public fun test_zero_amount_rejected(user: &signer) {
    my_module::deposit(user, 0); // Should abort
}

#[test(user = @0x1)]
#[expected_failure(abort_code = my_module::E_AMOUNT_TOO_HIGH)]
public fun test_excessive_amount_rejected(user: &signer) {
    my_module::deposit(user, my_module::MAX_DEPOSIT_AMOUNT + 1); // Should abort
}

#[test(owner = @0x1)]
#[expected_failure(abort_code = my_module::E_EMPTY_NAME)]
public fun test_empty_string_rejected(owner: &signer) {
    let obj = my_module::create_my_object(owner, string::utf8(b"Initial"));
    my_module::update_object(owner, obj, string::utf8(b"")); // Empty - should abort
}

#[test(owner = @0x1)]
#[expected_failure(abort_code = my_module::E_NAME_TOO_LONG)]
public fun test_string_too_long_rejected(owner: &signer) {
    let obj = my_module::create_my_object(owner, string::utf8(b"Initial"));

    // String exceeding MAX_NAME_LENGTH
    let long_name = string::utf8(b"This is an extremely long name that exceeds the maximum allowed length");

    my_module::update_object(owner, obj, long_name); // Should abort
}

#[test(owner = @0x1)]
#[expected_failure(abort_code = my_module::E_ZERO_ADDRESS)]
public fun test_zero_address_rejected(owner: &signer) {
    let obj = my_module::create_my_object(owner, string::utf8(b"Object"));
    my_module::transfer_object(owner, obj, @0x0); // Should abort
}

Step 5: Write Edge Case Tests

Test boundary conditions:

#[test(user = @0x1)]
public fun test_max_amount_allowed(user: &signer) {
    my_module::init_account(user);

    // Exactly MAX_DEPOSIT_AMOUNT should work
    my_module::deposit(user, my_module::MAX_DEPOSIT_AMOUNT);

    // Verify
    assert!(my_module::get_balance(signer::address_of(user)) == my_module::MAX_DEPOSIT_AMOUNT, 0);
}

#[test(user = @0x1)]
public fun test_max_name_length_allowed(user: &signer) {
    // Create string exactly MAX_NAME_LENGTH long
    let max_name = string::utf8(b"12345678901234567890123456789012"); // 32 chars if MAX = 32

    // Should succeed
    let obj = my_module::create_my_object(user, max_name);
}

#[test(user = @0x1)]
public fun test_empty_collection_operations(user: &signer) {
    let collection = my_module::create_collection(user, string::utf8(b"Collection"));

    // Should handle empty collection gracefully
    assert!(my_module::get_collection_size(collection) == 0, 0);
}

Step 6: Verify Coverage

Run tests with coverage:

# Run all tests
aptos move test

# Run with coverage
aptos move test --coverage

# Generate detailed coverage report
aptos move coverage source --module <module_name>

# Verify 100% coverage
aptos move coverage summary

Coverage report example:

module: my_module
coverage: 100.0% (150/150 lines covered)

If coverage < 100%:

Check uncovered lines in report
Write tests for missing paths
Repeat until 100%

Test Template Structure

#[test_only]
module my_addr::module_tests {
    use my_addr::module::{Self, Type};

    // ========== Setup Helpers ==========

    fun setup_default(): Object<Type> {
        // Common setup code
    }

    // ========== Happy Path Tests ==========

    #[test(user = @0x1)]
    public fun test_basic_operation_succeeds(user: &signer) {
        // Test happy path
    }

    // ========== Access Control Tests ==========

    #[test(owner = @0x1, attacker = @0x2)]
    #[expected_failure(abort_code = E_NOT_OWNER)]
    public fun test_unauthorized_access_fails(
        owner: &signer,
        attacker: &signer
    ) {
        // Test access control
    }

    // ========== Input Validation Tests ==========

    #[test(user = @0x1)]
    #[expected_failure(abort_code = E_INVALID_INPUT)]
    public fun test_invalid_input_rejected(user: &signer) {
        // Test input validation
    }

    // ========== Edge Case Tests ==========

    #[test(user = @0x1)]
    public fun test_boundary_condition(user: &signer) {
        // Test edge cases
    }
}

Testing Checklist

For each contract, verify you have tests for:

Happy Paths:

Object creation works
State updates work
Transfers work
All main features work

Access Control:

Non-owners cannot modify objects
Non-admins cannot call admin functions
Unauthorized users blocked

Input Validation:

Edge Cases:

Maximum values work
Minimum values work
Empty states handled

Coverage:

100% line coverage achieved
All error codes tested
All functions tested

ALWAYS Rules

✅ ALWAYS achieve 100% test coverage
✅ ALWAYS test error paths with #[expected_failure(abort_code = E_CODE)]
✅ ALWAYS test access control with multiple signers
✅ ALWAYS test input validation with invalid inputs
✅ ALWAYS test edge cases (boundaries, limits, empty states)
✅ ALWAYS use clear test names: test_feature_scenario
✅ ALWAYS verify all state changes in tests
✅ ALWAYS run aptos move test --coverage before deployment

NEVER Rules

❌ NEVER deploy without 100% coverage
❌ NEVER skip testing error paths
❌ NEVER skip access control tests
❌ NEVER use unclear test names
❌ NEVER batch tests without verifying each case
❌ NEVER hardcode real private keys or account addresses in test code — use test addresses like @0x1, @0x100, @0xCAFE
❌ NEVER read .env or ~/.aptos/config.yaml to get test addresses

Common Pitfalls

Struct Field Access Across Modules

Problem: Test modules cannot access struct fields from other modules directly.

// ❌ WRONG - Will NOT compile
let listing = marketplace::get_listing(nft_addr);
assert!(listing.price == 1000, 0);  // ERROR: field access not allowed

Solution: Use public view accessor functions from the main module.

// ✅ CORRECT - Use accessor function
let (seller, price, timestamp) = marketplace::get_listing_details(nft_addr);
assert!(price == 1000, 0);

If the module doesn't have accessors, add them:

// In main module
#[view]
public fun get_listing_details(nft_addr: address): (address, u64, u64) acquires Listings {
    let listing = table::borrow(&listings.items, nft_addr);
    (listing.seller, listing.price, listing.listed_at)
}

Escrow Pattern Error Expectations

Problem: After listing an NFT to escrow, the seller no longer owns it.

// ❌ WRONG expectation
#[expected_failure(abort_code = marketplace::E_ALREADY_LISTED)]
public fun test_cannot_list_twice(seller: &signer) {
    list_nft(seller, nft, 1000);  // NFT transfers to marketplace
    list_nft(seller, nft, 2000);  // Fails with E_NOT_OWNER, not E_ALREADY_LISTED!
}

Solution: Understand validation order - ownership is checked before listing status.

// ✅ CORRECT expectation
#[expected_failure(abort_code = marketplace::E_NOT_OWNER)]
public fun test_cannot_list_twice(seller: &signer) {
    list_nft(seller, nft, 1000);  // NFT transfers to marketplace
    list_nft(seller, nft, 2000);  // Seller doesn't own it -> E_NOT_OWNER
}

Acquires Annotation Errors

Problem: Adding acquires for resources borrowed by framework functions causes errors.

// ❌ WRONG - framework handles its own acquires
public entry fun stake(...) acquires VaultConfig, Stakes, StakeTokenRefs {
    primary_fungible_store::transfer(...);  // Don't list what framework borrows
}

Solution: Only list resources YOUR code borrows.

// ✅ CORRECT
public entry fun stake(...) acquires VaultConfig, Stakes {
    let config = borrow_global<VaultConfig>(...);  // You borrow this
    primary_fungible_store::transfer(...);          // Framework handles its own
}

References

Pattern Documentation:

../../../patterns/move/TESTING.md - Comprehensive testing guide (see Pattern 8 for cross-module issues)
../../../patterns/move/SECURITY.md - Security testing requirements

Official Documentation:

https://aptos.dev/build/smart-contracts/book/unit-testing

Related Skills:

write-contracts - Generate code to test
security-audit - Verify security after testing

Remember: 100% coverage is mandatory. Test happy paths, error paths, access control, and edge cases.

generate-tests