craigtp

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:
   Probability CombinedWith(Probability)
   Probability InverseOf()
   Probability Either(Probability)

if you forget your probability math:
   Either:P(A) + P(B) - P(A)P(B)
   CombinedWith: P(A)P(B)

craigtp

OK so now you have implemented the kata. Your tests should look something like this:

We can say that the tests define the object "in a calculus of itself".
They are not state based tests, they define how the behaviours of the object interact with each other.

To see the real value of this let's introduce some change ... I hear real system's do this occasionally.
Because this is a high performance system decimal math is too slow. You now need to use floats instead. 

Need help on floating point math? Check out: http://www-users.math.umd.edu/~jkolesar/mait613/floating_point_math.pdf

craigtp

Advanced Distributed System Design Course - Udi Dahan

Notes by Craig Phillips

Fallacies of Distributed Computing

• There are 11 fallacies of Distributed Computing:
  1. The network is reliable
  2. Latency isn’t a problem
  3. Bandwidth isn’t a problem
  4. The network is secure

5. The topology won’t change