Kata for "Greg Young's Probability Kata"
Value objects are an important concept in DDD. This kata is made both to learn value objects and to learn better ways of testing.
Write a probability value object. It should contain the following methods:
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Probability CombinedWith(Probability)
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Probability InverseOf()
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Probability Either(Probability)
if you forget your probability math:
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Either:P(A) + P(B) - P(A)P(B)
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CombinedWith: P(A)P(B)
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InverseOf: 1 - P(A)
The math is surprisingly not the main part of the exercise.
The internal state should be held as a decimal. Use TDD when writing this object.
One last thing. You can't put any getters on the object. What's the first test to write?
When finished continue reading: https://gist.github.com/1018566