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Dependable Software Systems: Syntax Testing & Formal Methods, Exams of Computer Science

Drexel UniversityComputer Science

Dependable software systems with a focus on syntax testing and formal methods. Topics include system inputs, validation, the million monkey phenomenon, input-tolerance testing, syntax testing steps, backus-naur form (bnf), telephone number example, sources of syntax, dangers of syntax test design, design automation, random string generators, formal specification, specification in the software process, formal specification on trial, advantages of formal specification, pre/post condition examples, set theory review, and pre/post conditions with java and c functions.

Typology: Exams

Pre 2010

Uploaded on 08/19/2009

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koofers-user-9ac 🇺🇸

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Dependable Software Systems (Syntax Testing & Formal Methods)
Dependable Software Systems (Syntax Testing & Formal Methods)
Dependable Software Systems
Topics in Syntax Testing
Formal Methods
Material drawn from [Beizer] Courtesy Spiros Mancoridis
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Dependable Software Systems

Topics in Syntax Testing

Formal Methods

Material drawn from [Beizer] Courtesy Spiros Mancoridis

Syntax Testing

  • System inputs must be validated. Internal

and external inputs conform to formats:

  • Textual format of data input from users.
  • File formats.
  • Database schemata.
  • Data formats can be mechanically converted

into many input data validation tests.

  • Such a conversion is easy when the input is

expressed in a formal notation such as BNF

(Backus-Naur Form).

Million Monkey Phenomenon

  • A million monkeys sit at a million

typewriters for a million years and

eventually one of them will type Hamlet!

  • Input validation is the first line of defense

against a hostile world.

Input-Tolerance Testing

  • Good user interface designers design their

systems so that it just doesn’t accept

garbage.

  • Good testers subject systems to the most

creative “garbage” possible.

  • Input-tolerance testing is usually done as

part of system testing and usually by

independent testers.

Automation is Necessary

  • Test execution automation is essential for

syntax testing because this method produces

a large number of tests.

How to Find the Syntax

  • Every input has a syntax.
  • The syntax may be:
    • formally specified
    • undocumented
    • just understood
  • … but it does exist!
  • Testers need a formal specification to test

the syntax and create useful “garbage”.

BNF Example

  • Correct phone numbers:
    • 3469900, 9904567, 3300000
  • Incorrect phone numbers:
    • 0551212, 123, 8, ABCDEFG special_digit ::= 0 | 1 | 2 | 5 other_digit ::= 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 ordinary_digit ::= special_digit | other_digit exchange_part ::= ordinary_digit number_part ::= phone_number ::= exchange_part number_part 2 other _ digit 4 ordinary _ digit

Why BNF?

  • Using a BNF specification is an easy way to

design format-validation test cases.

  • It is also an easy way for designers to

organize their work.

  • You should not begin to design tests until

you are able to distinguish incorrect data

from correct data.

Testing Strategy

  • Create one error at a time, while keeping all

other components of the input string correct.

  • Once a complete set of tests has been

specified for single errors, do the same for

double errors, then triple, errors, ...

  • Focus on one level at a time and keep the

level above and below as correct as you can.

Example: Telephone Number

(Level 1)

  • phone_number ::= exchange_part number_part
    • Empty string.
    • An exchange_part by itself.
    • Two from exchange_part.
    • Two from number_part.
    • One from exchange_part and two from number_part.
    • Two from exchange_part and one from number_part.
    • ...

Example: Telephone Number

(Level 2)

  • Bad number_part :
  • number_part ::= ordinary_digit
    • Not enough from ordinary_digit.
    • Too many from ordinary_digit.
    • ... 4

Example: Telephone Number

(Level 3)

  • ordinary_digit ::= special_digit | other_digit
    • Not a digit - alphabetic.
    • Not a digit - control character.
    • Not a digit - delimiter.
    • ...

Delimiter Errors

  • Delimiters are characters or strings placed

between two fields to denote where one

ends and the other begins.

  • Delimiter Problems:
    • Missing delimiter. e.g., (x+y
    • Wrong delimiter. e.g., (x+y]
    • Not a delimiter. e.g., (x+y 1
    • Poorly matched delimiters. e.g., (x+y))

Sources of Syntax

  • Designer-Tester Cooperation
  • Manuals
  • Help Screens
  • Design Documents
  • Prototypes
  • Programmer Interviews
  • Experimental (hacking)