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Code Contracts from Microsoft Research

Code Contracts provide a language-agnostic way to express coding assumptions in .NET programs. The contracts take the form of preconditions, postconditions, and object invariants. Contracts act as checked documentation of your external and internal APIs. The contracts are used to improve testing via runtime checking, enable static contract verification, and documentation generation.

Code Contracts bring the advantages of design-by-contract programming to all .NET programming languages. The benefits of writing contracts are:

Improved testability

  • each contract acts as an oracle, giving a test run a pass/fail indication.
  • automatic testing tools, such as Pex, can take advantage of contracts to generate more meaningful unit tests by filtering out meaningless test arguments that don’t satisfy the pre-conditions.

Static verification We have prototyped numerous static verification tools over the past years. Our current tool takes advantage of contracts to reduce false positives and produce more meaningful errors.

API documentation Our API documentation often lacks useful information. The same contracts used for runtime testing and static verification can also be used to generate better API documentation, such as which parameters need to be non-null, etc.

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