Difference between White box and Black box testing

Difference between White box and Black box testing

Criteria	Black Box Testing	White Box Testing
Definition	Black box testing is the Software testing method the internal structure/design/implementation of the item being tested is NOT known to the tester.	White box testing is the software testing method in which internal structure/design/implementation of the item being tested is known to the tester.
Levels Applicable To	Mainly applicable to higher levels of testing: Acceptance Testing, System Testing	Mainly applicable to lower levels of testing: Unit Testing, Integration Testing
Responsibility	Generally, independent: Software Testers	Generally, independent: Software Developers
Programming Knowledge	Not Required	Required
Implementation Knowledge	Not Required	Required
Basis for Test Cases	Requirement Specifications	Detail Design

Black Box Testing

Black Box Testing

• Black-box testing also called behavioral testing,
• It focuses on the functional requirements of the software.
• Functional testing of a component of a system
• Examine behavior through inputs & the corresponding outputs.
• Input is properly accepted, output is correctly produced.
• Black-box testing attempts to find errors in the following categories:
• (1) Incorrect or missing functions
• (2) Interface errors
• (3) Errors in data structures or external database access
• (4) Behavior or performance errors
• (5) initialization and termination errors
• Black box testing is used during the later stages of testing after white box testing has been performed.
• Different Black box testing techniques
• (1) Graph Based Testing Methods
• (2) Equivalence Partitioning
• (3) Boundary Value Analysis
• (4) Orthogonal Array Testing

Black box testing techniques - (1) Graph-Based Testing Methods

• The first step in black-box testing is to understand the objects that are modeled in software and the relationships that connect these objects.
• Once this has been accomplished, the next step is to define a series of tests that verify “all objects have the expected relationship to one another”.

• Graph Representation
• A collection of nodes that represent objects,
• Links that represent the relationships between objects,
• Node weights that describe the properties of a node (e.g., a specific data value or state behavior),
• Link weights that describe some characteristic of a link.
• The symbolic representation of a graph is shown in Figure.
• Nodes are represented as circles connected by links that take a number of different forms.
• A directed link (represented by an arrow) indicates that a relationship moves in only one direction.
• A bidirectional link, also called a symmetric link, implies that the relationship applies in both directions.
• Parallel links are used when a number of different relationships are established between graph nodes.  

Black box testing techniques - (2) Equivalence Partitioning Method

• Equivalence partitioning is a black-box testing method that divides the input domain of a program into classes of data from which test cases can be derived.
• An equivalence class represents a set of valid or invalid states for input conditions.
• Equivalence classes guidelines
• If an input condition specifies a range,
• one valid and two invalid equivalence classes are defined
• Input range: 1 – 10 Eq classes: {1..10}, {x < 1}, {x > 10}
• If an input condition requires a specific value,
• one valid and two invalid equivalence classes are defined
• Input value: 250 Eq classes: {250}, {x < 250}, {x > 250}
• If an input condition specifies a member of a set,
• one valid and one invalid equivalence class are defined
• Input set: {-2.5, 7.3, 8.4} Eq classes: {-2.5, 7.3, 8.4}, {any other x}
• If an input condition is a Boolean value,
• one valid and one invalid class are define
• Input: {true condition} Eq classes: {true condition}, {false condition} 

Black box testing techniques - (3) Boundary Value Analysis Technique

• A greater number of errors occurs at the boundaries of the input domain.
• It is for this reason that boundary value analysis (BVA) has been developed as a testing technique
• Test both sides of each boundary
• Look at output boundaries for test cases
• Test min, min-1, max, max+1, typical values
• Example : 1 <= x <=100
• Valid : 1, 2, 99, 100
• Invalid : 0 and 101
• Guidelines for BVA
• If an input condition specifies a range bounded by values a and b, test cases should be designed with values a and b and just above and just below a and b.
• If an input condition specifies a number of values, test cases should be developed that exercise the minimum and maximum numbers. Values just above and below minimum and maximum are also tested.

Black box testing techniques - (4) Orthogonal Array Testing

• Orthogonal array testing can be applied to problems in which the input domain is relatively small but too large to accommodate complete testing.
• The orthogonal array testing method is particularly useful in finding region faults — an error category associated with faulty logic within a software component.
• Consider a system that has three input items, X, Y, and Z. Each of these input items has three discrete values associated with it. There are 3^3 = 27 possible test cases.
• Phadke suggests a geometric view of the possible test cases associated with X, Y, and Z illustrated in Figure…
• Used when the number of input parameters is small and the values that each of the parameters may take are clearly

• To illustrate the use of the L9 orthogonal array, consider the send function for a fax application.
• Four parameters, P1, P2, P3, and P4, are passed to the send function. For example : Function (p1,p2,p3,p4)
• Each takes on three discrete values P1 takes on values:
• P1 = 1, send it now 
• P1 := 2, send it one hour later
• P1 = 3, send it after midnight
• P2, P3, and P4 would also take on values of 1, 2, and 3, signifying other send functions.
• If a “one input item at a time” testing strategy were chosen, the following sequence of tests (P1, P2, P3, P4) would be specified: (1, 1, 1, 1), (2, 1, 1, 1), (3, 1, 1, 1), (1, 2, 1, 1), (1, 3, 1, 1), (1, 1, 2, 1), (1, 1, 3, 1), (1, 1, 1, 2), and (1, 1, 1, 3).

The L9orthogonal array testing approach enables you to provide good test coverage with far fewer test cases than the exhaustive strategy

Black Box Testing - Advantage & Disadvantages

• Advantage
• Find missing functionality
• Independent from code size and functionality.
• Disadvantages
• No systematic search for low level errors.
• Specification errors not found.