The general goal of CVEs is to create a place for people to interact. This is a goal all CVEs have in common. CVEs must create a 3 dimensional space for its users, because of the intention of providing a place for users to manage their activities (Harrison & Dourish, 1996). It seems common sense to assume that the users need to feel present in this space in order to make sense of this 3 dimensional environment. For this reason presence and telepresence have received relatively much attention in the VR community (Tromp, 1995). CVEs also need to create a sense of co-presence, and a sense of being present in two or more environments at the same time. One of the consequences of presence in CVEs is that users of a typical CVE may have more than one embodiment in more than one CVE, and they always have to share their attentional resources between their real body in their real environment, and their virtual embodiment in the CVE.
The specific goal of CVEs always involves multiple tasks, not one single task. Users are working in a shared space in which they have to coordinate multiple activities. Because of the collaborative nature of CVEs, it is not sufficient to test for usability of one task. Instead, usability testing needs to address how multiple users are handling multiple, simultaneous tasks, and additionally it needs to look at their satisfaction and performance on executing and switching between these tasks. Which particular tasks these are depends on the specific goal of the application. For instance, in a CVE intended for virtual conferencing, the tasks become introducing oneself, establishing relationships, running a meeting, writing on the blackboard, observing behaviour of other participants, distributing information amongst the participants, etc.
Harrison, S., Dourish, P., (1996). Re-Place-ing Space: The Roles of Place and Space in Collaborative Systems, in Proceedings of CSCW'96.
Tromp, J.G., (1995). Presence, Telepresence, and Immersion; The Cognitive Factors of Embodiment and Interaction in Virtual Environments, in: Proceedings of the FIVE conference, Frameworks for Immersive Virtual Environments, December 18-19, London, UK.