In an ink! contract I need to use Self.env().block_number() to get the current block number to compare it with a block_number_guessed value that I provide when instantiating the contract and check that it is less than the current block number.

impl MyContract {
    pub fn new(
        block_number_guessed: BlockNumber,
    ) -> Self {
        let mut instance = Self::default();
        let block_number_current = Self::env().block_number();
            block_number_current > block_number_guessed,
            "block number when guessing occurred must be before the current block number"

I have written a test but I don't know how to provide a fake value of Self.env().block_number() in the unit tests to pretend that the current block number is greater than the fake value of 100 that I have used for block_number_guessed so that the assertion in the implementation when the contract is instantiated is satisfied and the test passes.

mod tests {
    use super::*;

    use crate::my_contract::MyContract;

    /// We test a simple use case of our contract.
    fn it_works() {
        let block_number_guessed = 100;
        let mut my_contract = MyContract::new(

I tried to use a custom environment CustomEnvironment and a custom chain extension CustomBlocknumberExtension like mentioned here as shown in the below code snippet, but I don't know how to write the implementation of fake_current_block_number, and I don't know if this is even a valid way to solve the issue.

mod tests {
    use super::*;

    use crate::my_contract::MyContract;

    use ink::env::{

    pub trait CustomBlocknumberExtension {
        type ErrorCode = CustomBlocknumberError;

        #[ink(extension = 0x1111)]
        fn fake_current_block_number() -> BlockNumber>;

    /// An environment using default ink environment types
    #[derive(Debug, Clone, PartialEq, Eq)]
    #[cfg_attr(feature = "std", derive(scale_info::TypeInfo))]
    pub enum CustomEnvironment {}

    impl Environment for CustomEnvironment {
        const MAX_EVENT_TOPICS: usize =
            <ink::env::DefaultEnvironment as Environment>::MAX_EVENT_TOPICS;

        type AccountId = <ink::env::DefaultEnvironment as Environment>::AccountId;
        type Balance = <ink::env::DefaultEnvironment as Environment>::Balance;
        type Hash = <ink::env::DefaultEnvironment as Environment>::Hash;
        type Timestamp = <ink::env::DefaultEnvironment as Environment>::Timestamp;
        type BlockNumber = <ink::env::DefaultEnvironment as Environment>::BlockNumber;

        type ChainExtension = crate::CustomBlocknumberExtension;

    /// We test a simple use case of our contract.
    #[ink::test(env = crate::CustomEnvironment)]
    fn it_allows_use_of_stubbed_blocknumber() {
        assert_eq!(env().extension().fake_current_block_number(), 200);

I looked through all the ink! examples repository, but I can't find any that stub the ink! environment in their tests.

How should we stub the ink! environment function Self.env().block_number() so we can provide a fake value for the current block number in our unit tests?


1 Answer 1


There is advance_block function in the ink::env::test and you can do something like this:

fn advance_n_blocks(n: u32) {
    for _ in 0..n {
fn advance_block() {

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