Symfony version(s) affected: 4.4

Description
#32683 introduced a new ImageCaster on top of imagine/image.
Problem is that the feature is not tested at all, and optional features that rely on external vendors must particularly be tested (allows for early detection of incompatible versions etc..).

How to reproduce

Possible Solution
Add imagine/image to the VarDumper dev-requirements and write a unit test for the ImageCaster (see other caster test cases for inspiration).

Additional context