Basics

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

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.

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 boilerplate which we'll customize for our pallet-testing pallet.

Create a mock runtime to test your pallet

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

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

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

Configure the mock runtime

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

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

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

   parameter_types! {
     pub const MaxValue: u32 = 50;
   }
   
   impl pallet_testing::Config for Test {
     type RuntimeEvent = RuntimeEvent;
     type MaxValue = MaxValue;
   }

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

Setup and create tests

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

use super::*;

1. Test that errors work as intended:

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

2. Create a test that should work:

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

3. And another that should fail:

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

Run your tests

Execute the following command from your pallet's directory:

cargo test

Examples

• tests in pallet_template

• tests in the reward-coin example pallet

Related material

• Unit testing

• Testing a transfer function

• assert_ok!

• assert_err!