Prevents further assertions, types, styles, plugins, and themes from being added to the instance. Once frozen, the addAssertion, addType, addStyle, installTheme, and use methods will throw an exception.

Cloning a frozen instance is allowed, and clones will not be frozen initially. Creating a child is also possible, but the child won't support exportAssertion, exportType, and exportStyle because the parent expect is frozen. This means that some plugins cannot be installed into the child. To get around that, create a clone first.

The plan is to make the top-level expect (the main export of require('unexpected')) frozen as of Unexpected 11. The idea behind that is to help prevent multiple files in a test suite from affecting each other by forcing each file to create its own isolated clone.