Unit testing

Protostar lets you test standalone Cairo functions. This technique is referred to as unit testing. You should write as many unit tests as possible as these are much faster than integration tests.

Writing your first test

First, add the following code to the src/lib.cairo file:

fn sum(a: felt252, b: felt252) -> felt252 {
    return a + b;
}

Now, let's test this function. Create a file tests/test_sum.cairo:

use your_project_name::sum;

#[test]
fn test_sum() {
    assert(sum(2, 3) == 5, 'sum incorrect');
}

Now run your test using this command:

protostar test ./tests

You should see something like this:

Collected 2 suites, and 3 test cases (10.64)
[PASS] tests/test_sum.cairo test_sum (time=0.00s)
Test suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Seed:        2752673895
17:20:43 [INFO] Execution time: 5.0 s

Test collecting

Protostar collects all test suites specified under the path passed as an argument. You can pass either directory or a specific file. A test suite is every .cairo file with a name starting from test_ or ending with _test. Protostar considers as a test case each function, inside a test suite, with #[test] attribute.

danger

Test cases cannot return any values and cannot take any arguments.

Failing tests

Your tests fail when code panics. To write a test that fails, you will need to use panic function, here's how you do it:

use array::ArrayTrait;

// Single value in the panic payload
#[test]
fn test_panic_single_value() {
    let mut data = ArrayTrait::new();
    data.append('this one should fail');
    panic(data)
}

Of course, if any of the functions you call from tests panics, your test will fail as well.