One of the main reasons we adopt build tooling is to apply transformations to the code and assets that make up an application. Some transformations are general-purpose optimizations that can be applied to a whole application, like minification or compression. Others are more contextualized, like inlining images or extracting critical CSS. There are even fully application-specific transformations, like localization or ahead-of-time compilation.
When an application's code and resources are represented as a graph of dependencies, transformations can be applied based on a resource's type, where it is used, or the way it is referenced. These tests cover some of the most commonly-used transformations.