We generally think of testing as something applied to the final code (in Chapter 17, Design for Testability, we'll look at automated testing in detail). However, we can also apply a test to a SOLID design. The test is to replace a given class with an equivalent class to provide an alternative algorithm to accomplish the same purpose. If we've done our design job well, then a change to one class should have a minimal splash with few ripples.
As a concrete example, consider the Domino class shown earlier in this chapter, under the Interface Segregation Principle section. We used a NamedTuple to represent the pair of numbers. Some alternatives are possible:
- Use a frozenset to retain one or two distinct values. If there's one value in the set, the tile is actually a double, or spinner.
- Use a Counter to retain the counts for the values...
