CS 451 Software Engineering Winter 2009 Yuanfang Cai Room 104, - - PowerPoint PPT Presentation

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Drexel University

CS 451 Software Engineering Winter 2009

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Yuanfang Cai Room 104, University Crossings 215.895.0298 yfcai@cs.drexel.edu

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Software Testing Techniques

 FUNDAMENTALS

 The goal of testing is to find errors.  A good test is one that has a high probability of finding

an error.

 A good test is not redundant  A good test should be neither too simple nor to

complex.

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Black Box and White Box Testing



One can test an engineered product by:

1. Knowing the specified function that a product was designed to perform. 2. Knowing the internal workings of a product 

Black box testing alludes to tests that are conducted at the software interface.



A black box test examines some fundamental aspect of a system with little regard for the internal structure of the software.



White-box testing of software is predicated on close examination of procedural detail.

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White Box Testing

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White Box Testing



White box testing is sometimes called glass box testing.



White box testing uses the control structure described as part of the component level design to derive test cases.



Using white box testing methods, the software engineer can derive test cases that:

1. guarantee that all independent paths within a module have been exercised at least once. 2. exercise all logical decisions on their true and false sides. 3. execute all loops at their boundaries and within their

• perational bounds

4. exercise internal data structures to ensure their validity.

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Code Coverage

 Method Coverage  Statement Coverage  Branch Coverage  Condition Coverage

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Method Coverage

 All methods have been called  Test Case 1: f(0, 0, 0) = 0

float f(int a, int b, int c) { if (a == 0) return 0; int x = b / a; if ((a == b || b == c) && (x != c)) x = -c; return 1.f / x; }

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Statement Coverage

 All “statements” have been executed  Test Case 1: f(1, 1, 1) = -1

float f(int a, int b, int c) { if (a == 0) return 0; int x = b / a; if ((a == b || b == c) && (x != c)) x = -c; return 1.f / x; }

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Branch Coverage

 All branches have been taken at least once  Test Case 1: f(1, 0, 0) = NaN

float f(int a, int b, int c) { if (a == 0) return 0; int x = b / a; if ((a == b || b == c) && (x != c)) x = -c; return 1.f / x; }

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Condition Coverage

 All predicates have been both true and false  Test Case 1: f(1, 1, 2) = -0.5

float f(int a, int b, int c) { if (a == 0) return 0; int x = b / a; if ((a == b || b == c) && (x != c)) x = -c; return 1.f / x; }

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Basis Path Testing



The basis path method enables the test case designer to derive a logical complexity measure of a procedural design and use this measure as a guide for defining a basis set of execution paths.



Test cases derived to exercise the basis set are guaranteed to execute every statement in the program at least one time during testing.

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Basis Path Testing



FLOW GRAPH NOTATION



A flow graph depicts logical control flow using the notation shown below:



Each structured construct corresponds to a flow graph symbol.

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Basis Path Testing



Flow charts and flow graphs correspond to

• ne another



The flow chart depicts the program control structure.



The flow graph assumes no compound structures.

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Basis Path Testing



Flow Graph



Each circle, called a flow graph node, represents

• ne or more procedural statements.



A sequence of process boxes and a decision diamond can map to a single node.



The arrows of a flow graph, called edges or links, represent flow of control.



An edge must terminate at a node.



Areas bounded by edges are called regions.

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Basis Path Testing

Flow Chart Flow Graph

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Basis Path Testing



Compound Conditions



Compound Conditions occur when one or more Boolean

• perators (OR, AND, NAND, NOR) is/are present in a

conditional statement.



IF A OR B is represented as follows:

Compound Logic:

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Basis Path Testing



Independent Program Paths



An independent program path is any path through the program that introduces at least one new set of processing statements or a new condition.



When stated in terms of a flow graph, an independent path must move along at least one edge that has not been traversed before the path is defined.

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Basis Path Testing

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For example, a set of independent paths for the flow graph illustrated in Figure 14.2b is:



Path 1: 1-11

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Path 2: 1-2-3-4-5-10-1-11



Path 3: 1-2-3-6-8-9-10-1-11



Path 4: 1-2-3-6-7-9-10-1-11

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Each new path introduces a new

• edge. Note the following path is

not independent:



1-2-3-4-5-10-1-2-3-6-8-9-10-1-11

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Basis Path Testing



A basis set for a flow graph is the set of paths that cover every statement in the program.



Therefore Paths 1, 2, 3, & 4 are the basis set for the previous figure.



If tests are designed to force execution of these paths, every statement is guaranteed to execute at least one

• time. Every condition will have been executed on its

true and false sides.



Note, a basis set is not unique. A number of basis sets may be derived from a procedural design.



How do we know how many paths to look for?

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Basis Path Testing

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Cyclomatic complexity is a software metric that provides a quantitative measure of the logical complexity of a program.



When used in the context of the basis path testing method, the value computed for cyclomatic complexity defines the number of independent paths in the basis set of a program and provides an upper bound for the number of tests that must be conducted to ensure that all statements have been executed at least once.

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Basis Path Testing

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Cyclomatic complexity is computed a number of ways:

1. The number of regions corresponds to the cyclomatic complexity. 2. Cyclomatic complexity, V(G), for a flow graph G, is defined as: V(G) = E – N + 2, where E is the number of flow graph edges, and N is the number of flow graph nodes. 3. Alternatively: V(G) = P + 1, where P is the number of predicate nodes contained in the flowchart G.

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Basis Path Testing

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Cyclomatic Complexity

1. The flow graph has 4 regions. 2. V(G) = 11 edges – 9 nodes +2 = 4 3. V(G) = 3 predicate nodes + 1 = 4

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Often components with a high V(G) are a high risk for error and should be tested more completely.

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Basis Path Testing

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Deriving Test Cases

1. Using the design or code as a foundation, draw a corresponding flow graph. 2. Determine the cyclomatic complexity of the resultant flow graph. 3. Determine a basis set of linearly independent paths. 4. Prepare test cases that will force execution of each path in the basis set.

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Basis Path Testing

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Figure 14.4

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Basis Path Testing

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Figure 14.4



V(G) = 6 regions



V(G) = 17 edges – 13 nodes + 2 = 6



V(G) = 5 predicate nodes + 1 = 6



Paths:



Path 1: 1-2-10-11-13

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Path 2: 1-2-10-12-13

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Path 3: 1-2-3-10-11-13

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Path 4: 1-2-3-4-5-8-9-2-…



Path 5: 1-2-3-4-5-6-7-8-2….



Path 6: 1-2-3-4-5-6-7-8-9-2… Prepare test cases that will force execution of each path in the basis set.

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Dealing With Loops

 Look for test cases to:

 Skip loop entirely  Go through loop once  Go through loop more than once

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Control Structure Testing

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Four different classes of loops:

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Control Structure Testing

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Four different classes of loops:

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Simple Loops: The following tests should be performed for simple loops, where n is the maximum number of allowable passes through the loop.

1. Skip the loop entirely 2. Only one pass through the loop 3. Two passes through the loop 4. M passes through the loop where m < n 5. N-1, n, n+1 passes through the loop

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Control Structure Testing



Four different classes of loops:

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Nested Loops:



If we extended the simple loop test cases to nested loops, the number of tests would grow geometrically.



Instead use the following scheme:

1. Start at the innermost loop. Set all other loops to their minimum values. 2. Conduct simple loop tests for the innermost loop while holding the

• uter loops at their minimum iteration parameter. Add other tests

for out-of-range or excluded values. 3. Work outward, conducting tests for the next loop, but keeping all the other outer loops at minimum values and other nested loops to “typical” values. 4. Continue until all loops have been tested.

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Control Structure Testing



Concatenated Loops

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Concatenated loops can be tested using the approach defined for simple loops, if each of the loops is independent of each other.

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If the two loops are concatenated and the loop counter for loop 1 is used as an initial value of loop 2, then the loops are not independent.



Unstructured Loops

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Whenever possible, this class of loops should be redesigned to reflect the use of the structured programming constructs.

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Summary

 Flow graph vs. Flow chart  Cyclomatic Complexity  Independent Path  Code Coverage  Test cases