How does violating the SOLID principles make code hard to test?

SOLID is the acronym form of the first five principle of object oriented programming. It basically provide the high cohesive units and used in the testing purpose. The SOLID principle combined together to develop a software easily and it is easy to maintain.

By applying the SOLID principle it makes easy to understand it also provide the better quality in the software. Therefore, violating the SOLID principle it become difficult the code to test.