Because they don't just implement a part of the interface (just one store method, or just one of two load methods). They try to create a fully functional fake of the original class.
In this case instead of storing the blobs via a REST interface or a database connection, it just keeps it in memory. So it should mostly behave like the real implementation, but is not suitable for production, as it doesn't persist the data.
The only things that are missing there are real life latency or maybe exceptions because of connectivity issues.
In this case instead of storing the blobs via a REST interface or a database connection, it just keeps it in memory. So it should mostly behave like the real implementation, but is not suitable for production, as it doesn't persist the data.
The only things that are missing there are real life latency or maybe exceptions because of connectivity issues.