1. Reliable Objects: Lightweight Testing for OO Languages
David Mattingly

2. Problems addressed Based on waterfall model – not on iterative models.
No longer feasible to separate testing from specification, design, coding.
Not based upon inherent power of OO.

3. Specifying behavior
Must know what each component should do in every situation
No formal specification language

4. Design by Contract Lightweight descriptions
Captures mutual obligations and benefits
Must specify every consistency condition
Boolean assertions

5. Implementation Implementations exist in Eiffel, Java, C++, Perl.
Eiffel only language to directly support design by contract.
All other languages rely on outside utilities.

6. Java Implementation
Example from Pylon library (
Source code with self-testable classes at

7. Java Design by Contract
Contract Watchdogs
trace and assert

8. Implementation 1 Call inherited functions directly in code.
Another level of inheritance.
Calls inside methods can be forgotten about.

9. Implementation 2 Contract definition in comments Preprocessor
iContract (

10. Making self-testable classes
Define pre and post-conditions in comments.
Interface inheritance and Delegation.
Testing methods: testing unit & goal

11. Validation & Verification
Compile with iContract & Java compiler.
Output details results of tests.

12. Abstract Classes Cannot be self-testable Can define contracts
Implementing classes inherit contracts

13. Mutation Testing Determine how adequate our tests our.
Adequate Test set distinguishes the original program from mutants.