Black Box testing techniques

Black Box Testing is testing technique having no knowledge of the internal functionality/structure of the system. This testing technique treats the system as black box or closed box. Tester will only know the formal inputs and projected results. Tester does not know how the program actually arrives at those results. Hence tester tests the system based on the functional specifications given to him. That is the reason black box testing is also considered as functional testing. This testing technique is also called as behavioral testing or opaque box testing or simply closed box testing. Although black box testing is a behavioral testing, Behavioral test design is slightly different from black-box test design because the use of internal knowledge is not illegal in behavioral testing

Black Box Testing has many types of techniques like:

1. Decision Table

Decision tables are a precise yet compact way to model complicated logic. Decision tables, like if-then-else and switch-case statements, associate conditions with actions to perform. But, unlike the control structures found in traditional programming languages, decision tables can associate many independent conditions with several actions in an elegant way.
Decision tables make it easy to observe that all possible conditions are accounted for. In the example above, every possible combination of the three conditions is given. In decision tables, when conditions are omitted, it is obvious even at a glance that logic is missing. Compare this to traditional control structures, where it is not easy to notice gaps in program logic with a mere glance --- sometimes it is difficult to follow which conditions correspond to which actions!
Just as decision tables make it easy to audit control logic, decision tables demand that a programmer think of all possible conditions. With traditional control structures, it is easy to forget about corner cases, especially when the else statement is optional. Since logic is so important to programming, decision tables are an excellent tool for designing control logic.

2. Equivalence Partitioning

The testing theory related to equivalence partitioning says that only one test case of each partition is needed to evaluate the behaviour of the program for the related partition. In other words it is sufficient to select one test case out of each partition to check the behaviour of the program. To use more or even all test cases of a partition will not find new faults in the program. The values within one partition are considered to be "equivalent". Thus the number of test cases can be reduced considerably.
Types of Equivalence Classes
* Continuous classes run from one point to another, with no clear separations of values. An example is a temperature range.
* Discrete classes have clear separation of values. Discrete classes are sets, or enumerations.
* Boolean classes are either true or false. Boolean classes only have two values, either true or false, on or off, yes or no. An example is whether a checkbox is checked or unchecked.
Equivalence partitioning is no stand alone method to determine test cases. It has to be supplemented by boundary value analysis. Having determined the partitions of possible inputs the method of boundary value analysis has to be applied to select the most effective test cases out of these partitions.

3. Boundary Value Analysis

Boundary value analysis is a software testing design technique to determine test cases covering off-by-one errors. The boundaries of software component input ranges are areas of frequent problems. Testing experience has shown that especially the boundaries of input ranges to a software component are liable to defects.
To set up boundary value analysis test cases you first have to determine which boundaries you have at the interface of a software component. This has to be done by applying the equivalence partitioning technique. Boundary value analysis and equivalence partitioning are inevitably linked together.
The tendency is to relate boundary value analysis more to the so called black box testing which is strictly checking a software component at its interfaces, without consideration of internal structures of the software. But looking closer at the subject, there are cases where it applies also to white box testing.
After determining the necessary test cases with equivalence partitioning and subsequent boundary value analysis, it is necessary to define the combinations of the test cases when there are multiple inputs to a software component.

4. Use Case Method

A use case is a technique used in software and systems engineering to capture the functional requirements of a system. Use cases describe the interaction between a primary actor—the initiator of the interaction—and the system itself, represented as a sequence of simple steps. Actors are something or someone which exist outside the system under study, and who (or which) take part in a sequence of activities in a dialogue with the system, to achieve some goal: they may be end users, other systems, or hardware devices. Each use case is a complete series of events, from the point of view of the actor.
Each use case provides one or more scenarios that convey how the actor will interact with the system to achieve a specific business goal or function. Use cases typically avoid technical jargon, preferring instead the language of the end user or domain expert. Use cases are often co-authored by systems analysts and end users. They are separate and distinct from UML use case diagrams, which allow one to abstractly work with groups of use cases.
A use case should:
* describe how the system shall be used by an actor to achieve a particular goal.
* have no implementation-specific language.
* be at the appropriate level of detail.
* Not include detail regarding user interfaces and screens. This is done in user-interface design.

5. State Transition Tables

In automata theory and sequential logic, a state transition table is a table showing what state (or states in the case of a nondeterministic finite automaton) a finite semiautomaton or finite state machine will move to, based on the current state and other inputs. A state table is essentially a truth table in which some of the inputs are the current state, and the outputs include the next state, along with other outputs. A state table is one of many ways to specify a state machine, other ways being a state diagram, and a characteristic equation.

6. Cross-functional testing
7. Pairwise testing