The General Principles of Software Validation; Final Guidance for Industry and FDA Staff from 2002 state: Software testing starts with unit testing (section 5.2.5). The General Principles emphasise test case creation, with defined inputs that can be compared to their predefined outcomes. The expected result is considered as an essential element of the test case. All this conforms to the philosophy behind Tessy.

The General Principles also state: Structural testing is accomplished primarily with unit (module) level testing. Tessy determines during unit testing both branch/decision coverage and even Multi-Condition Coverage (MCC) which is mentioned in the General Principles. Equivalence partitioning and boundary value analysis are recommended as means to generate test cases. This is incorporated in Tessy by means of the Classification Tree Method respectively the Classification Tree Editor (CTE).

If software is modified, regression testing is required by the General Principles, for which Tessy is well-suited because of the automation of the tests and the easy adaptation of the test cases to modified software.