Set up basic tests | Substrate

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

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

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--*/
```

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::*;

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"
   );
 })
}

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)
   );
 })
}

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