Most of the elements that make up an eXpress model (such as objects, ports, nets, functions, failure modes and effects) exist to document the operational behavior of a system or device (how it does or doesn't work). Tests, on the other hand, are used to represent the design's diagnostic behavior. Specifically, a test definition in eXpress is used to describe the diagnostic conclusions that can be reached when an individual test passes or fails. The primary purpose of the tests in eXpress is not to describe how a design can be tested, but rather to document the first-level diagnostic conclusions that can be drawn from that testing. Tests are created within test sets—groups that help keep tests organized and that can be separately selected for use in diagnostics. Following are Links to each type of test and links to operations with tests.
Types of Tests
There are 11 types of tests in eXpress. Each utilizes a different approach to testing. The reason to choose one type of test over another is to minimize the work needed to define the test and also to minimize the diagnostic effort to breakdown ambiguity within the model. For some test types, eXpress automatically computes test coverage). Test selection can significantly reduce the amount of effort required to describe the diagnostic knowledge inherent to given a test Selecting the right test type. The following 11 test types are supported within eXpress. Shown below are the Icons for each type and a link to the apllicable test type definition. Note: User-Defined Inferences (Special Licence) is not covered in this help file.
eXpress has the capability to set up functions to allow many tests to be generated at one time used primarily but not restricted to FPGA's and Processors. This capabilty can save many manhours of work. See Test Port Functions for [FPGAs, Processors]
Test Symmetry, Coverage & Interference
When examining how eXpress interprets different tests, it is important to understand the concept of symmetry that is inherent to each type of test. An inherently symmetric test is a test for which the output functions that are proven good when that test passes are the same as those that are indicted when the test fails. An inherently asymmetric test, then, is a test that indicts a different set of functions when it fails than those that are proven good when the test passes. In order to further understand the effect that inherent test symmetry has upon fault detection and isolation, refer to the topics above for each type of test. In addition to test symmetry, test definitions in eXpress are based on the concepts of coverage and interference. A test's coverage is the set of functions and/or failure modes that the test was intended to test. Test interference, on the other hand, is the degree to which other failures can interfere with the ability of a test to report its outcome ("good" or "bad"). This is critical to the test definition because diagnostics must factor in the potential ambiguity that can result from interference.
