Abstract : Testing is an important activity of the software development process. The aim of the work presented in this thesis is to free the test expert from repetitive aspects, relative to the test synthesis activity. Our approach, within the framework of conformance testing, is based on the fact that there are various levels of abstraction to define tests executable tests relative to a given technology, abstract tests relative to the specification level, and test purposes which describe some forms of expected behaviours. Our work adresses two main topics. The first one aims to decrease the test synthesis effort. We propose a new level of test definition : test schemas which abstract from instances of objects, and methods invocations. The TObiAs Tool was designed to support the definition of test schemas, their unfolding into abstract test cases or test purposes, and the generation of executable tests. The second contribution of the thesis evaluates the scope of a test schemas from a coverage measure of the level of the specification. We present the connection between the different levels of abstraction and how they can be interpreted to establish a notion of coverage of the specification. We present how we can build a coverage based on test schemas on an abstract specification and how we can use this new coverage with the CoPAS tool which we created to calculate the cover a priori.