Jest

Jest is a JavaScript unit testing framework that is used primarily for testing JavaScript applications built using Node or React. Jest provides a testing sandbox for parallel test management to prevent conflicts. It is a ‘zero configuration’ tool that also provides useful reports, like test code coverage (although Blaze is using SonarCloud to manage test coverage and code quality).

Jest also provides a powerful mocking library, which automatically mocks dependencies and allows tests to be run in a fake DOM implementation, facilitating Blaze interface development for developers. 

Blaze uses Jest extensively in CI pipelines for unit testing components and logic, ensuring that frequent deployments do not introduce regressions or errors.

License: Open Source (MIT)