Writing unit tests pytest

Titanoboa integrates natively with pytest and hypothesis. Nothing special is needed to enable these, as the plugins for these packages will be loaded automatically. By default, isolation is enabled for tests - that is, any changes to the EVM state inside the test case will automatically be rolled back after the test case completes.

Since titanoboa is framework-agnostic any other testing framework should work as well.

Let's cover the basics of testing with boa and pytest.

Let's start with a simple example contract Example.vy:

Vyper

foo: public(uint256)

@external
def set_foo(foo: uint256):
    self.foo = foo

We want to test that the set_foo function works correctly. That is, given an input, it should set the foo variable to the input value.

In the same folder as Example.vy, we create a file test_example.py:

We first create a pytest fixture that will deploy the contract:

Python

import pytest
import boa

@pytest.fixture
def example():
    return boa.load("Example.vy")

We can then write a test for the set_foo function, we can use example fixture to get an instance of the contract:

Python

def test_set_foo(example):
    example.set_foo(50)
    assert example.foo() == 50

We can run the test by calling pytest:

Bash

> pytest test_example.py
============================= test session starts ==============================
...
collected 1 item

test_example.py::test_set_foo PASSED

============================== 1 passed in 0.01s ===============================

Titanoboa Plugin

Titanoboa offers a pytest plugin that automatically resets the environment after each test. This is useful to isolate each test and avoid side effects between them. By using fixtures, pytest is able to correctly deploy the necessary contracts to run each specific test.

However, this can give errors when testing in network/fork mode. Most importantly, some RPCs will not support the evm_snapshot and evm_revert methods, which are used to reset the state after each test.

To disable the plugin, you may add the ignore_isolation marker.

Python

import pytest

# this will ignore the isolation for all tests in this file
pytestmark = pytest.mark.ignore_isolation

# this will ignore the isolation for this specific test
@pytest.mark.ignore_isolation
def test_set_foo(example):
    example.set_foo(50)
    assert example.foo() == 50

See more details in the environment explanation.