Setting up tests for your pallet

Get into the habit of writing tests as you write your pallet — it's good practice!

Goal#

Learn how to setup the scaffolding required to write tests for your pallet.

Use cases#

Writing and running unit tests for a pallet.

Overview#

This guide steps through how to use mock.rs and test.rs as a basis for testing your pallet. We'll be using the node template for the scaffolding of the mock.rs file and an arbitrary pallet — called pallet-testing — to give this guide some context. This pallet will contain a single function called add_value, that takes an origin and a u32 and returns Ok(()) if the value is less than or equal to a constant called MaxValue that we specify in the mock runtime.

Steps#

1. Use the template node as boilerplate#

Inside pallet-testing/src, the first thing we need to do is create two empty files: mock.rs and tests.rs.

Paste in the contents from template/src/mock.rs. We'll use this as boilerpate which we'll customize for our pallet-testing pallet.

2. Create a mock runtime to test your pallet#

Start by modifying pallet-testing/src/mock.rs to include the pallet-testing pallet. This involves changes in the following code sections:

Dependencies#

Replace the first line with the name of the pallet, in our case pallet_testing:

use crate as pallet_testing;
/*--snip--*/

Configure mock runtime#

In frame_support::construct_runtime!, replace pallet_template with the name of your pallet, in our case pallet_testing:

/*--snip--*/
    TestingPallet: pallet_testing::{Module, Call, Storage, Event<T>},
/*--snip--*/

Implement your pallet for the mock runtime#

Replace impl pallet_template::Config for Test {...} with the your configuration types and any constant values your pallet requires:

parameter_types! {
    pub const MaxValue: u32 = 50;
}

impl pallet_testing::Config for Test {
    type Event = Event;
    type MaxValue = MaxValue;
}

To put the mock runtime to use, we need to set up our tests.rs file for the pallet-testing pallet.

3. Setup and create tests#

In tests.rs, start by importing the dependencies you'll need from lib.rs using super:

use super::*;

Testing that errors work#

This will test whether the error works as intended:

#[test]
fn error_works(){
    new_test_ext().execute_with(|| {
        assert_err!(
            TestingPallet::add_value(Origin::signed(1), 51),
            "value must be <= maximum add amount constant"
        );
    })
}

Testing known working case#

Create a test that should work:

#[test]
fn test_should_work() {
    new_test_ext().execute_with(|| {
        assert_ok!(
            TestingPallet::add_value(Origin::signed(1), 10)
        );
    })
}

Testing known failing case#

And another that should fail:

#[test]
fn test_should_fail() {
    new_test_ext().execute_with(|| {
        assert_ok!(
            TestingPallet::add_value(Origin::signed(1), 100)
        );
    })
}