unit testing

Aleksey Tyulpin, NArFU, [email protected]

Unit testingBasics, Test Driven Development

Plan● Basics of Unit testing● Nose framework● Exercise● Test driven development

What is testing?● Testing is the process of executing a program with the intent of finding

errors. (Mayers 1979)

● Software testing is a formal process carried out by a specialized testing team in which a software unit, several integrated software units or an entire software package are examined by running the programs on a computer. All the associated tests are performed according to approved test procedures on approved test cases.

(Galin 2004)

What is testing?● Program testing can be used to show the presence of

bugs, but never their absence(Dijkstra 1972)

● Central question of software testing is “what is a test criterion?”

(Goodenough and Gerhart [1975, 1977])

Software testing objectives● Direct

○ To identify and reveal as many errors as possible in the tested software.

○ To bring the tested software, after correction of the identified errors and retesting, to an acceptable level of quality.

○ To perform the required tests efficiently and effectively, within budgetary and scheduling limitations.

● Inderect○ To compile a record of software errors for use in error prevention (by

corrective and preventive actions).(Galin 2004)

Unit Testing● Unit testing (UT) is a method for modular testing of a

program’s functional behavior● Program is decomposed into units - collection sof

functions● Units are independently tested● Such testing requires specification of values for the

inputs (or test inputs) to the unit(Koushik Sen, Darko Marinov, Gul Agha 2005)

A.A.A. Phases● Arrange - prepare test. Step includes preparation of

input data and expected result● Act - call what you test● Assert - compare the result of called method (or

function) to the expected result

Nose framework● Simple possible failing test:

def test():assert False

● Simple passing test:def test():

pass

● Nose collects tests automatically from python source files, directories and packages found in its working directory

● For running tests you have to use tool nosetests:nosetests3 [options] [(optional) test files or directories]

● I prefer to use such command:nosetests3 -v

How to write tests ● Every test should be simple and perform on one set of input data● Name of every test should explain what test checks● Remember about A.A.A. phases ● Name test modules/files starting with ‘test_’● Name test functions starting with ‘test_’● Example:

def test_MultiplyShouldRetun12For3And4():a, b = 3,4 # Arrangeres = multiply(a,b) # Actassert res == 12 # Assert

Palindrome checker ● In your home directory there is a folder - Dev/nose_palindrome● In this floder there is a module which contains function isPalidrome(word),

where variable word is a string.○ Example

>>> import palindrome as p>>> p.isPalindrome('kazak')True

● Task - write tests and find as many bugs as possible. All possible kinds of tests are allowed.

Test Driven Development● Kent Beck, 2003● Steps:

○ Add fail-test○ Write code○ Run test○ Refactor the code

● Writing only the code necessary to pass tests

● Writing the tests first drives a deeper and earlier understanding of the product requirements

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