A legacy codebase that resist a bit testing.

First try to run it.

Then your goal is to make it testable so that you can make changes (FIXME inside) and perhaps refactor it a bit.

This code draws on a C# code kata authored by my distinguished colleague Nicolas M.; Thanks Nicolas for the good ideas in the kata!

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If you hesitate where to start, here are some of the tricky bits that make it hard to test:

Lack of dependency injection:

• A static main with no args
• Static service
• Hard-coded instantiation of a service that itself instantiates its dependencies, and again

Implementation issues:

• Very slow service
• Hidden dependency to a license key in env variable
• Random return value -> non-deterministic test
• Dialog poping up prompting for user input

Other tricks:

• New Date() in the middle of calculations -> non-deterministic test
• High combinatorial of calculations lead to too many required test cases
• Stateful behavior from internal cache: first call different from next calls
• Heavy dependency called within a large loop with different values
• Use a dependency or another depending on the passed parameter