We focus on the implications of movement, landscape variables, and spatial heterogeneity for food web dynamics. Movements of nutrients, detritus, prey, and consumers among habitats are ubiquitous in diverse biomes and can strongly influence population, consumer-resource, food web, and community dynamics. Nutrient and detrital subsidies usually increase primary and secondary productivity, both directly and indirectly. Prey subsidies, by movement of either prey or predators, usually enhance predator abundance beyond what local resources can support. Top-down effects occur when spatially subsidized consumers affect local resources by suppressing key resources and occasionally by initiating trophic cascades. Effects on community dynamics vary with the relative amount of input, the trophic roles of the mobile and recipient entities, and the local food web structure. Landscape variables such as the perimeter/area ratio of the focal habitat, permeability of habitat boundaries, and relative productivity of trophically connected habitats affect the degree and importance of spatial subsidization.

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T he test-driven development strategy requires writing automated tests prior to developing functional code in small, rapid iterations. Although developers have been applying TDD in various forms for several decades, 1 this software development strategy has continued to gain increased attention as one of the core extreme programming practices.XP is an agile method that develops object-ori ented software in very short iterations with little upfront design. Although not originally given this name, TDD was described as an integral XP prac tice necessary for analysis, design, and testing that also enables design through refactoring, collective ownership, continuous integration, and programmer courage.Along with pair programming and refactoring, TDD has received considerable individual attention since XP's introduction. Developers have created tools specifically to support TDD across a range of languages, and they have written numerous books explaining how to apply TDD concepts. Re searchers have begun to examine TDD's effects on defect reduction and quality improvements in aca demic and professional practitioner environments, and educators have started to examine how to inte grate TDD into computer science and software engineering pedagogy. Some of these efforts have been implemented in the context of XP projects, while others are independent of them. TEST-DRIVEN DEVELOPMENT DEFINEDAlthough its name implies that TDD is a testing method, a close examination of the term reveals a more complex picture.

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Test-driven development (TDD) is