Incorporation of test functionality into software components

COTS components trustworthiness is a key issue to be addressed within the field of component-based software engineering. This problem relies on the duality between development and deployment. COTS components vendors may prove varied properties for their components but purchasers may want to validate these properties in different execution environments. Built-In Test is thus the ability to endow components with extra functionality in order to develop in-situ tests. This paper stresses a Java library that supports Built-In Contract Testing. Complex component behaviors are ruled and observed based on states and reactivity to client requests. A large component consisting in a Programmable Thermostat illustrates the Built-In Contract Testing technology and the offered Java library.