1

“White box” or “glass box” tests

“White Box” (or “Glass Box”) Tests

2

Basic goal of white box testing

White box testing--”lowest level”:Part of a comprehensive test plan—see fig. 11.1 in text

Test planning

developer userclient

Unit tests

Integration tests

Structure tests

Functional tests

Performance tests

User test

activities

Clienttest

activities

3

Path testing

General method 1: Path testing or basis path testing

basic goal: make sure all paths in the control structure of a unit are tested at least once

why?

1. "bad code" is more likely in rarely executed paths

2. what we think is a "rare" path may turn out to be taken a lot

3. syntax errors can occur anywhere

4

White box testing--example

example:integer a,b,count=0;input a,b;if (a == 0) while (b > 0) {b = b-1; count++;}else if (a > 0) while (b < 0) {b = b+1; count--;}else a = b;output a,b,count;

What (minimal) set of tests would make sure that all paths are tested in this code?

Are there other test cases that would be advisable?

5

White box testing requirements

what needs to be tested:

1. all independent paths must be followed at least once

2. all logical decisions must have both true and false input

3. all loops must be executed at boundaries and within their bounds

4. all internal data structures must be used

6

Basis path method

This method guarantees that every statement will be executed at least once

Flow graph: • node represents one or more statements• edges represent control flow, as in flowcharts

Example: flow graphs for control structures:

Sequential

If

Until

While

Case

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Basis path method (continued)

Determine number of tests needed:

a.develop a "flow graph" G--make graph for basic control structure--sequential statements with no branches in or out can be

merged into one statement

b.compute the "cyclotomic complexity”: V(G) = E - N + 2, where E = #edges, N = #nodes

or V(G) = number of planar regions defined by the graph

V(G) is an upper bound on the number of "independent" paths through the code which must be followed through an appropriate choice of test cases in order to execute every statement at least once

NOTE: this gives the number of paths for the GRAPH; program structure may mean a smaller number of paths is actually needed

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Basis path method--example

Example:integer a,b,count=0; //1input a,b; //2if (a == 0) //3 while (b > 0) //4 {b = b-1; //5 count++;} //6else if (a > 0) //7 while (b < 0) //8 {b = b+1; //9 count--;} //10else //11 a = b; //12output a,b,count; //13

Flow chart:1

2

3

4

5

6

7

8

9

10

11

12

13

11,12

1,2,3

5,6

4 7

9,10

8

13

Flow graph:E=11,N=8;E-N+2=55 paths

Tests:a b0 20 -11 -11 2-1 -1

* 1 edge,multiple paths

*

*

*

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Basis path method—6 steps

1. Number lines of executable code:integer a,b,count=0; //1input a,b; //2if (a == 0) //3 while (b > 0) //4 {b = b-1; //5 count++;} //6else if (a > 0) //7 while (b < 0) //8 {b = b+1; //9 count--;} //10else //11 a = b; //12output a,b,count; //13

2. Construct flow chart:

1

2

3

4

5

6

7

8

9

10

11

12

137

9,10

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3. Construct flow graph:

4. Compute upper bound on number of paths: E=11,N=8; E-N+2=5;5 paths

5. Determine tests:

a 0 0 1 1 -1 b 2 -1 -1 2 -1

11,12

1,2,3

5,6

4

136. Add additional tests (e.g., let b=0)

Note; treat a function call (including a recursive call) as ONE statement, don’t expand

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Basis path method--augmentations

Basis path method can also be used with a “graph matrix” to automate the generation of test cases (Beizer, Software Testing Techniques, 1990):

Example: use the flow graph to define a graph matrix:

Entries can be, for example: --Edges (1 or 0) --Probability of execution --Time to traverse an edge --Memory needed to traverse edge --Resources needed to traverse edge

Values can be used to determine what

test cases should be run

1

4

3

25

1 2 3 4 5

1 1

2 1 1 1

3 1

4

5 1 1

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Data flow testing

General method 2: based on definition / redefinition of variables:

data flow testing: focuses on program variables x---e.g., require that every definition use chain (DU) be covered at least once

DU chains:for each program statement S

def(S)={x|x defined in S} and use(S)={x|x is used in S}

example: if S is the statement a = b + c then

def(S) = {a}; use(S) = {b,c}

x at S is live at S':there is a path from S to S' in which x is not redefined

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Def{S}, use{S}

Example: b = 3; //S

c = 4; //S'a = b + c; //S''d = a + b; //S'''

def(S) = {b}; def(S') = {c}; def(S'') = {a}; def (S''') = {d}

use(S) = ; use(S') = ; use(S'')= {b,c}; use(S''')={a,b}

a at S'' is live at S'''; b at S is live at S',S'', and S''';c at S' is live at S'';

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DU chains

definition use chain (DU) of x is [x,S,S'] where x is in def(S) and use(S') and def. of x in S is live at S'

so in this example:b = 3; //Sc = 4; //S'a = b + c; //S''d = a + b; //S'''

DU chains are:a: [a, S'', S'''] b: [b, S,S''] and [b,S,S'''] c: [c, S', S'']

testing: must cover every DU chain at least once

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DU chains--example

another simple example:0. input j,k;1. x = j; y = k;2. if (x > 0)3. y = y + 2;4. x = x + 5;5. endif6. z = x + y + 4;

DU chains:1-[j,0,1]; 2-[k,0,1]; 3-[x,1,2],4-[x,1,4],5-[x,1,6],6-[x,4,6]7-[y,1,3],8-[y,1,6],9-[y,3,6]

test cases:j = 4, k = 5;--covers 1,2,3,4,5,7,8 and j = -4, k = 5;--covers 6,9

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State-based testing

General method 3: state-based testing (text, p. 461):

Works well for object-oriented designs

Derives tests from component’s associated state machine diagram

Each transition in the diagram must be traversed at least once

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Example: Finite-state machine (FSM) model—what state transitions must be tested?

Idle

GoingUp

req > floor

req < floor

!(req > floor)

!(timer < 10)

req < floor

DoorOpen

GoingDn

req > floor

u,d,o, t = 1,0,0,0

u,d,o,t = 0,0,1,0

u,d,o,t = 0,1,0,0

u,d,o,t = 0,0,1,1

u is up, d is down, o is open

req == floor

!(req<floor)

timer < 10

t is timer_start

UnitControl process using a state machine

From Vahid/Grivargis, Embedded System Design, 2000

State-based testing (continued)

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Polymorphism testing

Polymorphism testing: Must be sure to identify and test all possible bindings, static and dynamic

Example: fig. 11-15

Network interface

UMTSWaveLANEthernet

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Additional white box testing

some methods to broaden the test coverage:

condition testing: add tests for each value of a given condition (e.g., if (a == c and b == d) )

domain testing: for each relational expression (a relational-operator b) generate tests for cases: a < b, a = b, a > b

loop testing: simple loops (max # of iterations = n):skip it one passtwo passesm passes, m < nn-1, n, n+1 passes

(8 <= # passes <= 4n+8)

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Additional white box testing (continued)

nested loops: tests can grow geometrically ( (n2))some reductions may be used (see p. 458, Pressman)

concatenated loops:if loops are not independent, should treat as nested loops

unstructured loops: avoid these in your design and code

Nested loops Concatenated loops

Unstructured loops (to be avoided)