TRex– The Refactoring and Metrics Tool for TTCN-3 Test Specifications

 Abstract

Comprehensive testing of modern communication system soften requires large and complex test suites which then have to be maintained throughout the system life-cycle. Industrial experience, with those written in the standardised Testing and Test Control Notation (TTCN-3), has shown that this maintenance is a non-trivial task and its burden could be reduced if appropriate tool support existed. To this aim, Motorola has collaborated with the University of Gottingen to develop TRex, a TTCN-3 development environment published under the Eclipse Public License, which notably provides suitable metrics and refactorings to enable the assessment and automatic restructuring of test suites. In this paper we present the TRex tool, which will make it far easier to construct and maintain TTCN-3 tests that are concise and optimally balanced with respect to readability, usability, and maintainability.

1.Introduction

The Testing and Test Control Notation(TTCN-3)[3,5]is a test specification and test implementation language standardised by the European Telecommunications Standards Institute (ETSI) and the International Telecommunication Union (ITU). While TTCN-3 has its roots in functional black-box testing of telecommunication systems, it is nowadays also used in other domains such as Internet protocols, automotive, aerospace, or service-oriented architectures. TTCN-3 can be used not only for specifying and implementing functional tests, but also for scalability, robustness or stress tests. TTCN-3 is based on a textual core notation and several presentation formats.

Commercial TTCN-3 tools [7,8,11] support editing test suites and compiling them into executable code. By implementing the interfaces of the standardised TTCN-3 runtime environment, these tools may also allow TTCN-3 test campaigns to be managed and executed.

However, experience within Motorola has shown that not only editing and execution of TTCN-3 test suites, but also maintenance and assessment of these are important issues which require tool support [1]. It is not always obvious how to use TTCN-3 concepts such as templates in a manner that can maximise readability, usability and maintainability, so user guidance and assistance in these areas would be extremely beneficial. In addition, Motorola teams have encountered related problems whilst migrating legacy test suites to TTCN-3; the conversion of tests for a UMTS based component to TTCN-3 initially resulted in 60,000 lines of code which were hard to read, hard to (re-)use, and hard to maintain, as the benefits of moving to TTCN-3 were not yet being fully exploited. In legacy modelling languages the specification of data values is often tightly coupled with the behaviour specification, i.e. when a signal is sent between processes, the value of the signal is defined within the behaviour of each process. This means that when the signal type is modified, each behaviour definition must also be modified and value definitions cannot easily be reused. In this case the task of manually decoupling data from behaviour to improve maintainability, whilst also reducing suite size by merging commonalities and hence improving readability, proved to be particularly challenging and time-consuming.

Currently, no tools for assessing and improving the quality of TTCN-3 test suites exist. To this end, Motorola has collaborated with the University of Gottingen to develop a TTCN-3 refactoring and metrics tool, called TRex. The initial aims of TRex were to: (1) enable the assessment of a TTCN-3 test suite with respect to lessons learnt from experience, (2) provide a means of detecting opportunities to avoid any issues, and (3) a means for restructuring TTCN-3 test suites to improve them with respect to any existing issues. To let others participate in our tool and to participate in contributions from others, we have made TRex a general open-source quality assurance and quality improvement tool for TTCN-3 test suites.

This paper is structured as follows: In the next section, we will give an overview of TRex’s functionality following with a description of the implementation in Section 3. In Section 4 we conclude with a summary and outlook.

2.Functionality of the TRex tool

TRex is implemented as an Eclipse plug-in and therefore, anyone who has had experience with the Eclipse Platform [2], e.g. by using the popular Java Development Tools (JDT), will immediately feel comfortable with TRex. The TTCN-3 perspective of TRex allows editing of TTCN-3 core notation as well as assessing and improving the quality ofTTCN-3 test suites.
2.1. Editing
TRex provides editing facilities known from a typical Integrated Development Environment (IDE). These include a Navigator view for project browsing, an editor with syntax high lighting and checking according to the latest TTCN-3 core language specification (v3.1.1), an Outline view providing a tree representation of the TTCN-3 structure for the currently edited file, Content Assist which automatically completes identifiers from their prefix and scope, a code-formatter, a reference finder which displays all references to a given element, and the possibility to jump to the declaration of a given reference. In addition, to allow the edited tests to be compiled and run against either a real or emulated system under test, the Telelogic Tau G2/Tester [8] analyser and compiler t3cg is integrated into the TRex environment.

2.2. Refactoring
As a powerful means for improving the quality of TTCN-3 test suites, TRex is able to restructure test suites in an automated way. This is achieved by using refactoring which is defined as “a change made to the internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior” [4].While refactoring is well known for implementation languages like Java, it has not been systematically studied for TTCN-3. Thus, we developed a catalogue of 49 refactorings applicable for TTCN-3 [13, 14]. In TRex, we have begun implementing those refactorings which we believe would improve the maintainability of Motorola’s test suites and have so far completed the Inline Template, Inline Template Parameter, Merge Templates, and Rename refactorings. As an example, we will describe the Inline Template refactoring in detail.

For specifying test data, TTCN-3 uses so called templates. A template may either be defined as a named entity on its own or “on-the-fly” using an inline template notation. The first way promotes re-use since a template definition may be referenced at several locations. In contrast, test behaviour may be easier to understand if it uses inline templates, since inline templates define test data at the same location where it is actually used for sending or receiving. Inline Template refactoring allows a template reference to be transformed into its semantically equivalent inline template notation. The application of this refactoring is particularly reasonable if a template is only referenced once. When applying this refactoring to a template reference, TRex opens a wizard dialogue which offers configuration for the Inline Template refactoring. As shown in Figure1 (a), it is possible to remove the declaration of a template if it was referenced only once and the Formatter may additionally be used to obtain a pretty-printed template. Before a refactoring is actually applied, the refactoring wizard displays a preview of all resulting changes (Figure 1(b)).

These refactorings are typically semi-automated, since the user still has to identify locations where they should be applied (as known from JDT for example). However, as shown in the next section, TRex can also automatically identify such locations.

2.3. Metrics
As part of TRex we are investigating the application of metrics to give an indication of both the overall quality of a TTCN-3 test suite and any locations where it might be beneficial to apply a particular refactoring.

We have implemented basic size metrics in the TRex tool, including Number of... and References to... for various definitions and types as well as a measure, labelled Template coupling, of the dependency between test behaviour and test data (in the form of template definitions). Figure 2(a) showstheTTCN-3 Metrics view.

Based on these metrics, we have defined several rules by which the templates of a TTCN-3 test suite can be analysed, e.g. looking at number of references, use of parameters, commonalities, etc. From these, TRex is able to identify problematic code fragments and to suggest suitable refactorings. For example, templates which could be removed, in lined, or merged into a common parametrised version. These suggestions are displayed in the Problems view as warnings (Figure 2(c)) and can either be treated merely as indicators that should be taken into account whilst working on the test suite, or an associated Quick Fix can be invoked via the context menu to perform a suggested refactoring automatically (Figure 2(b)). A full description of our metrics and rules is available in our previous paper on TTCN-3 refactoring [14].

3. Implementation of the TRex tool

Building an IDE on Eclipse is attractive from the developer’s point of view as it is well documented and supported, and provides many ready-to-use components. Such components include project and file management (workspace)and a graphical user interface (workbench) which can be configured to match the typical layout of an IDE. In fact, the majority of TRex’s functionality is built upon abstract implementations provided by Eclipse. Figure 3 shows the TRex tool chain: the Eclipse Platform provides the basic IDE infrastructure. The TRex components build on top of the Eclipse Platform. They are explained in the subsequent sections.

3.1. Static analysis

The foundation for most functionality in TRex is the TTCN-3 parser and the resulting syntax tree . For building up the syntax tree for a test suite we use ‘Another Tool for Language Recognition’ (ANTLR) [9], a parser generator which supports lexing, parsing, and syntax tree creation
and traversal. For tree traversal, ANTLR uses tree grammars (e.g. the pretty printer uses a tree grammar enriched with semantic actions for the syntax reconstruction).

Most of the advanced functionality of TRex requires additional information for TTCN-3 identifiers, such as the identifier’s type, or the syntax tree node of its declaration. To easily find this information, a symbol table was implemented. The syntax tree and the symbol table provide the basis upon which most of TRex’s present functionality is realised, e.g. the metrics and refactoring implementations both use them. As shown in Block (1) of Figure 3, the lexer creates a token stream from the TTCN-3 core notation which is used by the parser for syntactical validation and for building the syntax tree. In addition, the symbol table is also created here.

3.2. The refactoring implementation

The refactoring implementations make use of the Eclipse Language Toolkit(LTK) which provides abstract classes for semantic preserving workspace transformations and customisable wizard pages for the user interaction. The benefit of such wizard pages is, for example, an integrated preview pane that can be used to compare the original source to the refactored source side by side.

Block (2) in Figure 3 depicts how the automated refactorings are realised. On the basis of the static analysis step (Block (1)), the workspace transformations can be calculated once the concerned syntax tree node(or nodes respectively) has been found through a data structure which stores identifiers along with their text file offsets and once the user entered any required information in the refactoring wizard.

The transformation of the workspace resources (i.e. text files)is realised with a programmatic text edit or provided by the Eclipse Platform. It supports copy, paste, move, delete, insert, and replace operations. These operations are used to weave only the textually changed parts into the original TTCN-3 source files. Therefore most of the original formatting is preserved. In some cases an intermediate step involving a syntax tree transformation may become necessary, in order to calculate the required changes. In this case, the TTCN-3 core notation to be weaved into the original TTCN-3 source files is obtained by the pretty printer. Applying multiple changes to a single file is supported by the programmatic editor by automatically tracking changing offset positions.

3.3. Metrics and refactoring suggestions

Metrics are measured immediately after the syntax tree for a test suite has been built or updated (Block (3) in Figure 3). The tree is then fully traversed; all definitions that metrics will be calculated for (alt step, function, template, etc.) are recorded and all communication statements (send, receive, etc.) are processed to derive Template coupling scorings. References to all of these are calculated in a further pass of the tree, hence giving enough information for the basic size metrics (described in Section 2.3) to be displayed. Then all templates found in the first step are processed one-by-one against the analysis rules, using the previously calculated referencing information as well as further inspection of their structure.

Once this has completed, the rule findings are associated with the templates in the form of customised Eclipse marker objects which are automatically displayed in the Problems view. Quick Fixes are resolved for each of them based on extended attributes which indicate the detected situation and hence some corresponding suggestion(s) from the rule set.

4.Summary andoutlook

We presented TRex, an Eclipse-based TTCN-3 development environment with an emphasis on quality assessment and quality improvement of TTCN-3 test suites. TRex has been developed as a collaboration between Motorola and the University of Gottingen to address industrial demands by applying current research results. Besides editing functionality, TRex provides user-initiated semi-automated refactoring of TTCN-3 test suites, as well as fully automated refactoring based on special rules which interpret metric values.

Future versions of TRex will include enhanced editing capabilities and further metrics, refactoring, and analyses forTTCN-3testsuites. Therefore, we have started to implement control-flow- and call-graphs for TTCN-3 behaviour. These graphs will be used, for example, to provide complexity metrics and to allow the detection of anomalies in the control- and data-flow.

Even though TRex is still under development, we have already started our first experiments into the use of TRex for quality improvement and assessment. The results are very promising. For example, test suites consisting of many templates were reduced in size considerably by automatically removing unused templates and by merging similar templates into common parametrised versions. We have also started to analyse existing real-world TTCN-3 test suites in order to determine appropriate boundary values for our metrics. These boundary values are very important for the optima linterpretation of calculated metrics.

The use of metrics to assess the quality of TTCN-3 test suites and to suggest appropriate refactorings is only one possible approach. A further approach, which we would like to pursue in the future, is to identify anti-patterns, i.e. inappropriate usage of TTCN-3(so called “bad smells”). In contrast to the calculation of metrics, this requires a pattern-based approach, e.g.to identify duplicate code.

TRex is an open-source tool that is freely available under the Eclipse Public License at its web site[12]. In addition to the application of TRex in industry, TRex is also being used as a tool for academic research and teaching. We invite the TTCN-3 community to use the tool, share their experience, and participate in the future development of TRex.

Currently, we have defined the notion of quality of TTCN-3 test suites only in an informal manner: e.g. using inline templates reduces maintainability but improves readability (but only up to a certain size of a template) or parametrised templates promote reuse, but not necessarily maintainability or readability. However, as a solid foundation for test suite assessment and improvement a more formal quality model for test suites is desirable. For quality of software products in general, the International Organization for Standardization and the International Electro technical Commission have defined quality characteristic (functionality, reliability, usability, efficiency, maintainability, and portability), sub-characteristics, and metrics for measuring attributes of these characteristics [6]. Thus, for future work the challenge remains to investigate the applicability of this existing quality model to test specifications.