Black Box Unit Testing

1209

What is black-box testing?

• Unit (code, module) seen as a black box

• No access to the internal or logical structure

• Determine if given input produces expected output.

Input Output

Black Box Testing

• Test set is derived from requirements • Goal is to cover the input space• Lots of approaches to describing input space:

– Equivalence Classes– Boundary Value Analysis– Decision Tables– State Transitions– Use Cases– . . .

Advantage and Disadvantage

• Advantage:

• Disadvantage:

• Need to define an efficient strategy to limit number of test cases

General Black Box Process

• Analyze requirements

• Select valid and invalid inputs

• Determine expected outputs

• Construct tests

• Run tests

• Compare actual outputs to expected outputs

Equivalence Relations:

• Reflexive

• Symmetric

• Transitive

Equivalence classes: Basic Strategy• Partition the input into equivalence classes

• Test a subset from each class

Basic strategy:

Example: fact(n): if n<0, or n>=200 errorif 0<=n<=20, exact valueif 20<n<200, approximate value within .1%

Simple Example:

• Suppose you are building an airline reservation system. A traveler can be a child, an adult, or a senior.

• The price depends on the type of traveler. • The seat reservation does not depend on the type

of traveler.• How many test cases are required for the

reservation component and the billing component?

Finding equivalence classes:

• Identify restrictions for inputs and outputs in the specification

• If there is a continuous numerical domain, create one valid and two or three invalid classes (above, below, and NaN)

• If a number of values is required, create one valid and two invalid classes

Boundary Values:

• Programs that fail at interior elements of a class usually fail at the boundaries too.

• Test the boundaries.

Hints

• If a domain is a restricted set, check the boundaries. e.g., D=[1,10], test 0, 1, 10, 11– It may be possible to test the boundaries of outputs,

also.

• For ordered sets, check the first and last elements• For complex data structures, the empty list, full

lists, the zero array, and the null pointer should be tested

Boundary Value: in class

• Determine the boundary values for US Postal Service ZIP codes

• Determine the boundary values for a 15- character last name entry.

Decision Tables

• Construct a table (to help organize the testing)

• Identify each rule or condition in the system that depends on some input

• For each input to one of these rules, list the combinations of inputs and the expected results

Decision Table Example

Test Case C1

Student

C2

Senior

Result

Discount?

1

2

3

4

Theater ticket prices are discounted for senior citizens and students.

Pairwise Testing

Problem 1From Lee Copeland, A Practitioner’s Guide to Software Test Design, Artech

House Publishers, 2004.

• A web site must operate correctly with different browsers: IE 5, IE 6, and IE 7; Mozilla 1.1; Opera 7; and FireFox 2, 3, and 4.

• It must work using RealPlayer, MediaPlayer, or no plugin.• It needs to run under Windows ME, NT, 2000, XP, and

Vista, and 7.0• It needs to accept pages from IIS, Apache and WebLogic

running on Windows NT, 2000, and Linux servers

Problem 2

• A bank is ready to test a data processing system• Customer types

– Gold (i.e., normal)– Platinum (i.e., important)– Business– Non profits

• Account types– Checking– Savings– Mortgages – Consumer loans– Commercial loans

• States (with different rules): CA, NV, UT, ID, AZ, NM

From Lee Copeland, A Practitioner’s Guide to Software Test Design, Artech House Publishers, 2004.

When given a large number of combinations: (options improve …)

• Give up and don’t test• Test all combinations … miss targets, delay

product launch, and go out of business• Choose one or two cases

Orthogonal Arrays

• A 2-D array with the property– All pairwise combinations occur in every pair of

columns

• Example: consider 3 variables (columns) with {a,b}, {1,2}, and (α,β)

1 2 3

1 1 A α

2 1 B β

3 2 A β

4 2 B α

Orthogonal Array Example

1 2 3

1 1 A α

2 1 B β

3 2 A β

4 2 B α

Look at each pair of columns (1 and 2),( 1 and 3), and (2 and 3)

Does each of the 4 pairings appear in each?

(Yes, of course!)

Pairwise Testing Algorithm

1. Identify variables

2. Determine choices for each variable

3. Locate an orthogonal array

4. Map test cases to the orthogonal array

5. Construct tests

Example using Bank

1. Identify variables

2. Determine choices for each variable

3. Locate an orthogonal array 4. Map test cases to the orthogonal array5. Construct tests

Locate an orthogonal array (look up on web)

1 1 1

1 2 2

1 3 3

1 4 4

2 1 2

2 2 1

2 3 4

2 4 3

3 1 3

3 2 4

3 3 1

3 4 2

4 1 4

4 2 3

4 3 2

4 4 1

5 5 1

5 1 2

5 2 3

5 3 4

6 5 2

6 1 1

6 2 4

6 3 3

1 5 3

2 5 4

3 5 1

4 5 2

5 4 1

6 4 2

Map Test Cases (30)CA Check Gold

CA Save Plat

CA Mort Busi

CA Cons NonP

NV Check Plat

NV Save Gold

NV Mort NonP

NV Cons Busi

UT Check Busi

UT Save NonP

UT Mort Gold

UT Cons Plat

ID Check NonP

ID Save Busi

ID Mort Plat

ID Cons Gold

AZ Comm Gold

AZ Check Plat

AZ Save Busi

AZ Mort NonP

NM Comm Plat

NM Check Gold

NM Save NonP

NM Mort Busi

CA Comm Busi

NV Comm NonP

UT Comm Gold

ID Comm Plat

AZ Cons Gold

NM Cons Plat

Pairwise Summary• When the combination is large, test all pairs,

not all combinations

• Studies indicate that most defects are single or double-mode effects – Can be found in pairing– Few defects require more than two modes

• Orthogonal arrays have the pairwise property and can be found or generated

State Transition Testing

State Transition Testing

• Build STD of system or component

• Cover the STD

Example

Res MadePaid

CancelledNon Pay

Ticketed

CancelledCust

Used

Cust Order/start timer

Payment madeTicket Printed

Time Expires

Ticket DeliveredCancel/refund

Cancel/refund

Cancel

Use Case Testing