A few guidelines are given below to identify test cases through generated equivalence classes:

• Assign a unique identification number to each equivalence class.
• Write a new test case covering as many of the uncovered valid equivalence classes as possible, until all valid equivalence classes have been covered by test cases.
• Write a test case that covers one, and only one, of the uncovered invalid equivalence classes, until all invalid equivalence classes have been covered by test cases. The reason that invalid cases are covered by individual test cases is that certain erroneous-input checks mask or supersede other erroneous-input checks. For instance, if the specification states 'Enter type of toys (Automatic, Mechanical, Soft toy) and amount $(1-10000)$' , the test case [ABC 0] expresses two error (invalid inputs) conditions (invalid toy type and invalid amount) will not demonstrate the invalid amount test case, hence the program may produce an output '$\mathrm{ABC}$ is unknown toy type' and not bother to examine the remainder of the input.

Remember that there may be many possible solutions for one problem in this technique, depending on the criteria chosen for partitioning the test domain.