Set up basic tests | Substrate

⚠️ Update Notice:

Please read Substrate to Polkadot SDK page first.

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