Equivalence Class Partitioning
  • Learn what is meant by equivalence partitioning
  • Design test cases using equivalence partitioning
    Concepts:   Equivalence partitioning is a method for deriving test cases.  In this
    method, classes of input conditions  called equivalence classes  are
    identified such that each member of the class causes the same kind of
    processing and output to occur. 
    In this method, the tester identifies various equivalence classes for partitioning.  A class
    is a set of input conditions that are is likely to be handled the same way
    by the system.  If the system were to handle one case in the class
    erroneously, it would handle all cases erroneously.
    Equivalence partitioning drastically cuts down the number of test cases
     required to test a system reasonably.  It is an attempt to get a good
     'hit rate', to find the most errors with the smallest number
     of test cases.
    To use equivalence partitioning, you will need to perform two steps
  • Identify the equivalence classes
  • Design test cases STEP 1: IDENTIFY EQUIVALENCE CLASSES Take each input condition described in the specification and derive at least two equivalence classes for it. One class represents the set of cases which satisfy the condition (the valid class) and one represents cases which do not (the invalid class ) Following are some general guidelines for identifying equivalence classes: a) If the requirements state that a numeric value is input to the system and must be within a range of values, identify one valid class inputs which are within the valid range and two invalid equivalence classes inputs which are too low and inputs which are too high. For example, if an item in inventory can have a quantity of - 9999 to + 9999, identify the following classes: 1. one valid class: (QTY is greater than or equal to -9999 and is less than or equal to 9999). This is written as (- 9999 < = QTY < = 9999) 2. the invalid class (QTY is less than -9999), also written as (QTY < -9999) 3. the invalid class (QTY is greater than 9999) , also written as (QTY >9999) b) If the requirements state that the number of items input by the system at some point must lie within a certain range, specify one valid class where the number of inputs is within the valid range, one invalid class where there are too few inputs and one invalid class where there are, too many inputs. For example, specifications state that a maximum of 4 purchase orders can be registered against anyone product. The equivalence classes are : the valid equivalence class: (number of purchase orders is greater than or equal to 1 and less than or equal to 4 , also written as (1 < = no. of purchase orders < = 4) the invalid class (no. of purchase orders> 4) the invalid class (no. of purchase orders < 1) c) If the requirements state that a particular input item match one of a set of values and each case will be dealt with the same way, identify a valid class for values in the set and one invalid class representing values outside of the set. For example, if the requirements state that a valid province code is ON, QU, and NB, then identify : the valid class code is one of ON, QU, NB the invalid class code is not one of ON, QU, NB d) If the requirements state that a particular input item match one of a set of values and each case will be dealt with differently, identify a valid equivalence class for each element and only one invalid class for values outside the set. For example, if a discount code must be input as P for preferred customer, R for standard reduced rate, or N for none, and if each case is treated differently, identify the valid class code = P the valid class code = R the valid class code = N the invalid class code is not one of P, R, N e) If you think any elements of an equivalence class will be handled differently than the others, divide the equivalence class to create an equivalence class with only these elements and an equivalence class with none of these elements. For example, a bank account balance may be from $0 up to $ 1,000,000, and balances $ 1,000 or over are not subject to service charges. Identify : the valid class: ($ 0 < = balance < $ 1,000) i.e., balance is between 0 and $ 1,000 - not including $ 1,000 the valid class: ($ 1, 000 < = balance < = $ 1,000,000 i.e., balance is between $ 1,000 and $1,000,000 inclusive the invalid class: (balance < $ 0) the invalid class: (balance> $ 1,000,000) A definition of Equivalence Partitioning from our software testing dictionary: Equivalence Partitioning: An approach where classes of inputs are categorized for product or function validation. This usually does not include combinations of input, but rather a single state value based by class. For example, with a given function there may be several classes of input that may be used for positive testing. If function expects an integer and receives an integer as input, this would be considered as positive test assertion. On the other hand, if a character or any other input class other than integer is provided, this would be considered a negative test assertion or condition.

  • Equivalence partitioning definition from From Wikipedia, the free encyclopedia.
    A technique in black box testing is equivalence partitioning. Equivalence
     partitioning is designed to minimize the number of test cases by dividing
     tests in such a way that the system is expected to act the same way for all
     tests of each equivalence partition. Test inputs would be selected from each partition.
    Equivalence partitions are designed so that every possible input belongs
     to one and only one equivalence partition.
    END Equivalence Class Partitioning

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    © January 2002 Alex Samurin http://www.geocities.com/xtremetesting/