César Andrés

Formal passive testing of timed systems: theory and tools

This paper presents a methodology to perform passive testing of timed systems. In passive testing, the tester does not interact with the implementation under test. On the contrary, execution traces are observed without interfering with the behaviour of the system. Invariants are used to represent the most relevant expected properties of the implementation under test. Intuitively, an invariant expresses the fact that each time the implementation under test performs a given sequence of actions, it must exhibit a behaviour in a lapse of time reflected in the invariant. There are two types of invariants: consequent and observational. The paper gives two algorithms to decide the correctness of proposed invariants with respect to a given specification and algorithms to check the correctness of a log, recorded from the implementation under test, with respect to an invariant. The soundness of this methodology is shown by relating it to an implementation relation. In addition to the theoretical framework, a tool called PASTE has been developed. This tool helps in the automation of the passive testing approach because it implements all the algorithms presented in this paper. PASTE takes advantage of mutation testing techniques in order to evaluate the goodness of an invariant according to its capability to detect errors in logs generated from mutants. An empirical study where PASTE was used to analyse a non‐trivial system is also reported. Copyright

Passive Testing of Timed Systems

This paper presents a methodology to perform passive testing based on invariants for systems that present temporal restrictions. Invariants represent the most relevant expected properties of the implementation under test. Intuitively, an invariant expresses the fact that each time the implementation under test performs a given sequence of actions, then it must exhibit a behavior in a lapse of time reflected in the invariant. In particular, the algorithm presented in this paper are fully implemented.

Trust-orBAC: A Trust Access Control Model in Multi-Organization Environments

Access control in Multi-Organization Environment is a critical issue. Classical access control models like Role Based Access Control (RBAC) and Organization Based Access Control (orBAC) need some improvements to be used in such environment, where the collaboration is established between organizations and not directly with the clients. In particular, some characteristics of this scenario are that the users may be unknown in advance and/or the behaviors of the users and the organization may change during the collaboration. Hence, in this context the use of trust management with an access control model is recommended.

Formal Correctness of a Passive Testing Approach for Timed Systems

In this paper we extend our previous work on passive testing of timed systems to establish a formal criterion to determine correctness of an implementation under test. In our framework, an invariant expresses the fact that if theimplementation under test performs a given sequence of actions, then it must exhibit a behavior in a lapse of time reflected in the invariant. In a previous paper we gave an algorithm to establish the correctness of an invariant with respect to a specification. In this paper we continue the work by providing an algorithm to check the correctness of a log, recorded form the implementation under test, with respect to an invariant. We show the soundness of our method by relating it to an implementation relation. In addition to the theoretical framework we have developed a tool, called PASTE, that facilitates the automation of our passive testing approach.

Passive testing of web services

This paper presents a methodology to perform passive testing based on invariants of distributed systems with time information. This approach is supported by the following idea: A set of invariants represents the most relevant expected properties of the implementation under test. Intuitively, an invariant expresses the fact that each time the system under test performs a given sequence of actions, then it must exhibit a behavior reflected in the invariant. We call these invariants local because they only check the correctness of the logs that have been recorded in each isolated system. We discuss the type of errors that are undetectable by using only local invariants. In order to cope with these limitations, this paper introduces a new family of invariants, called globals to deal with more subtle characteristics. They express properties of a set of systems, by making relations between the set of recorded local logs. In addition, we show that global invariants are able to detect the class of undetected errors for local invariants.

Passive Testing of Stochastic Timed Systems

In this paper we introduce a formal methodology to perform passive testing, based on invariants, for systems where the passing of time is represented in probabilistic terms by means of probability distributions functions. In our approach, invariants express the fact that each time the implementation under test performs a given sequence of actions, then it must exhibit a behavior according to the probability distribution functions reflected in the invariant. We present algorithms to decide the correctness of the proposed invariants with respect to a given specification. Once we know that an invariant is correct, we check whether the execution traces observed from the implementation respect the invariant. In addition to the theoretical framework we have developed a tool, called PASTE, that helps in the automation of our passive testing approach. We have used the tool to obtain experimental results from the application of our methodology.

Supporting the Extraction of Timed Properties for Passive Testing by Using Probabilistic User Models

Testing is one of the most widely used techniques to increase the quality and reliability of complex software systems. In this paper we extend our previous work on passive testing with invariants to incorporate (probabilistic) knowledge obtained from users of the system under test. In order to apply our technique, we need to obtain a set of invariants compiling the relevant properties of the system under test, and this is a time-intensive task. We present a novel approach to extract invariants from a specification, based on the idea that an invariant is better than another one if it can be checked more times in a given log. We present a formal approach where probabilistic user models are incorporated.

A vector based model approach for defining trust in Multi-Organization Environments

A Multi-Organization Environment is composed of several players that depend on each other for resources and services. In order to manage the security of the exchange process we introduce the concept of trust. We show how this aspect of the cooperative work allows us to increase some security aspects. In particular, we provide a framework where the concepts of trust requirement and trust evaluation play important roles for defining trust vectors. These vectors evaluate a set of requirements, under some conditions, and provide a degree of confidence. In our framework we consider two different types of vectors. On the one hand a vector that relates a user to an organization and on the other hand a vector that links two organizations. Finally we show how these vectors are evaluated and shared among the different organizations, and how we combine the provided trust information in order to enhance the security.

Applying Formal Passive Testing to Study Temporal Properties of the Stream Control Transmission Protocol

In this paper we present a formal passive testing framework and use it to analyze time aspects in the Stream Control Transmission Protocol (\SCTP). This protocol presents different phases where time aspects are critical. In order to represent temporal requirements we use so-called {\it timed invariants} since they allow us to easily verify that the traces collected from the observation of the protocol fulfill the corresponding timed constraints. In addition to introduce our theoretical framework, we report on the results obtained from the application of our techniques over (possibly mutated) traces extracted from runs of the SCTP.

Advantages of Mutation in Passive Testing: An Empirical Study

This paper presents an empirical study of the mutation techniques used by the tool PASTE. This tool allows the automation of our passive testing methodology for systems that present stochastic-time information. In our proposal, invariants express the fact that each time the implementation under test performs a given sequence of actions, then it must exhibit a behavior according to the probability distribution functions reflected in the invariant. We briefly review the theoretical framework of our methodology and the main features of our tool. Next, we present in detail the Mutants module that provides us with a functionality to test the effectiveness of invariants for detecting errors. Finally, we present a study of the results obtained from the performed experiments.