Mocking Kata – Copier (.NET)

To continue my series on Mocking Katas (see Mocking Kata – Instrument Processor for the last Kata), I’ll show you a very simple Kata that I normally use in my Test Driven Development training courses to introduce mocks (created manually or dynamically with the use of a mocking framework): the CharacterCopier.

Character Copier

The character copier is a simple class that reads characters from a source and copies them to a destination one character at a time.

The character copier gets the source and destination injected in the constructor.


When the method Copy is called on the copier then it should read characters from the source and copy them to the destination until the source returns a newline (‘\n’).

The exercise is to implement the character copier using mocks for the source and the destination (try using manually written mocks and mocks written with a mocking framework.

Points of Interest

The following points make this exercise interesting:

  • Good exercise to compare manually written mocks to generated ones.
  • Ordering of calls on destination is important
  • Small steps: first copy a single character, then multiples ending with \n
  • Very concise
    Happy mocking!

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Urs Enzler

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By Urs Enzler

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