Like Operational and User-Initiated tests, Probe tests are path-based tests whose coverage and stimuli are automatically determined using knowledge from the functional model. However, unlike the other types of path-based tests, a Probe test can be defined with an internal net (rather than an output flag) as the measurement location. The Analyst can also select which output functions are explicitly observed (provided that they are defined on ports that are connected to the same net). The test coverage is still filled out with all output functions in the design that are upstream from the specified measurement location and downstream from selected stimuli (and not omitted due to state selections). Individual output functions and failure modes can be removed from the coverage by marking them as non-detectable.
Probe tests also behave differently than Operational or User-Initiated tests when inherited hierarchically. The test point for the hierarchical test will remain that of the lower-level inherited test, although the stimuli will consist of inputs to the upper-level model. Additional upper-level coverage is added to the hierarchical test (upstream only from the inherited coverage) based on the new stimuli.
NOTE: The name "Probe test" does not mean to imply that a probe must be used in the real system to use this test. In today's distributed computing world most systems do integrated testing with the software points within the system (IBIT, PBIT etc.). Therefore the Probe test (which is an path based test) is a very good candidate for testing at a software point. Its advantage is that it does not require any additional effort when it is hierarchically used to indicate the observation point.
