This article will help you learn parameter definition strategies for creating the most efficient set of TCD tests.

Long lists of Values always result in large numbers of tests


  • Imagine you are testing an application that has a drop box with 500 city names
  • The application also has 5 different features that will be tested together with different cities
  • If you list each city individually and create a set of 2-way tests, the smallest possible number of tests you would generate would be 500 X 5 = 2,500 tests

Instead, define Equivalence Classes and enter them into Test Case Designer.

Depending upon the business rules and behaviors of the application you are testing, you might break your equivalence classes of cities into size-based categories or location-based categories such as these:

  • The population of city: under 1 million, 1 million – 2.99 million, 3 million – 8.99 million, Above 9 million


  • Location of the city: Asia, Americas, Europe, Africa, or Australia

If you reduced your list of city-related Values from 500 to 4, you would have far fewer pairwise tests generated when you click the Scenarios button.

For more information:

  • Don’t forget to explore TCD’s Value Expansion feature
  • See Wikipedia’s description of Equivalence Class Partitioning
  • A simple 2-minute experiment demonstrates how important this lesson is:
  1. Create 2 test models in Test Case Designer
  2. Call the first one “2p20v” (this automatically generates a model with 2 Parameters with 20 Values each)
  3. Call the second one “20p2v.”
  4. The first model has only 400 possible tests. All 400 tests are needed to achieve pairwise coverage.
  5. The second model has over a million possible tests. Only 11 tests are needed for pairwise coverage!

  • No labels