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In order to ensure that the new rolling stock can traverse over the new tracks at the new desired speed, each element (component) must be verified as being able to carry the rolling stock at the new desired speed. In other words each element making up the track system must be separately unit tested to verify their individual quality. Once the components have been assembled into a complete track system, a series of integration/system level tests must be executed to verify that the rolling stock can actually get to their destinations within a specified set of requirements. So from a software perspective unit level testing with tools like JUnit/NUnit verify the quality of the components in a system, and tools like fitnesse FitNesse verify that the system is built according the requirements (user acceptance testing), in other words you have built what I asked for (more of an end to end testing strategy).
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