Ranges of numbers (such as all numbers between 10 and 99, which are of the same two-digit equivalence class)
Membership in groups (dates, times, country names, ete.)
Invalid inputs (placing symbols into text-only fields, etc)
Equivalent output events (variation of inputs that produce the same output)
Equivalent operating environments
Repetition of activities
Number of records in a database (or other equivalent objects)
Equivalent sums or other arithmetic results
Equivalent numbers of items entered (such as the number of characters enterd into a field)
Equivalent space (on a page or on a screen)
Equivalent amount of memory, disk space, or other resources available to a program.
Boundary values mark the transition points between equivalence clases. They can be limit values that define the line between supported inputs and nonsupported inputs,or they can define the line between supported system requirements and nonsupported system requirements. Applications are more susceptible to errors at the boundaries of equivalence classs, so boundary condition tests can be quite effective at uncovering errors.
Generally, each equivalence class is partitioned by its boundary vakues. Nevertheless, not all equivalence classs have boundaries. For example, given the following four browser equivalent classes(NETSCAPE 4.6.1 and Microsoft Internet Explorer 4.0 and 5.0), thereis no boundary defined among each class.
Each equivalence class represents potential risk. Under the equivalent class approach to developing test cases, at most, nine test cases should be executed against each partition.
