To test a method, you have to instantiate or construct the class containing the method. The most common mistake developers make is to create what I call Monster Constructor, which is simply a constructor that does too much work or real work, such as performing I/O operations, database calls, static initialization, reading some large files, or establishing communication with external services.
When you have a class designed with a constructor that initializes or instantiates objects other than value objects (list, array, and dictionary), the class technically has a nonflexible structure. This is a bad class design because the class automatically becomes strongly tied to the classes it is instantiating, making unit testing ...
