Automated testing overview

February 2012

Summary

• Why do we need software testing• Software testing definition• Types of testing• Why do we need automated testing• Unit testing for simple objects• Unit testing for objects that have

dependencies• Automated testing for user interface

Why do we need software testing

• To reduce operating costs : software bugs are a big cost for the business;

• To protect company reputation : software quality is a key requirement of any new project;

• any developer will do some kind of testing before delivering the software to the client;

• software testing is a core activity associated with the development process;

Software testing definition

• Definition: Software testing is an investigation conducted to provide stakeholders with information about the quality of the product or service under test;

• software testing verifies and validates that the software deliverable:– meets the business and technical requirements that

guided its design and development;– works as expected;

Types of testing

• system testing : exercises the application end to end. Based on specifications and executed using tests scripts as part of a test plan.

• integration testing : targets parts of the application e.g. the service layer;

• unit testing : tests individual code units : e.g. classes.

Cost of software bugs

Cost to fix a defectTime detected

Requirements

Architecture

Construction

System test

After release

Time introduced

Requirements

1x 3x 5-10x 10x 10-100x

Architecture - 1x 10x 15x 25-100x

Construction - - 1x 10x 10-25x• the cost of removing a software bug is linked to the development stage the software bug is found;

Difficulties of software testing

• It is a lengthy process and can happen only after the alpha stage of the application;

• Constant retesting : After each release we need to test new features and retest existing ones - even if the changes affect only a part of the application we can never be sure that the rest of the application is unaffected;

• Usually the full test plan is applied right at the end of the delivery cycle : regression errors or unexpected errors can be detected too close to final delivery - they can affect the delivery schedule;

Solution: automated tests

• Automate the test plan right from the beginning of the development cycle : the developer can now exercise the application before is deployed to testing;

• System testing will always have a manual part but can be also comprised of automated tests that can cover a lot of scenarios

• Use unit testing and integration testing extensively as they can be automated with minimal costs;

Why do we need automated testing

• TIME - speed up the delivery schedule : the test window is reduced and testers can concentrate more on exploratory testing and test cases that cannot be automated;

• COST - reduce the number of bugs : bugs can be detected before a deployment is made and regression issues are reduced significantly;

• SCOPE - reduce the amount of rework and make scope changes cheap: the testers, business analysts and developers will start from test scenarios first that will increase the product knowledge right from the start;

How to implement automated tests

• The application need to be testable;• System testing : coded ui tests using an automation

framework or using record and replay tools;• Integrations tests : inject data that is used to exercise

the application layers for specific scenarios;• Unit testing : they are code only tests so they don’t

have an impact on external systems and their dependencies

Unit testing

What is a unit test

• Can I run and get results from a unit test I wrote two weeks or even months or years ago?

• Can any member of my team run and get the results from unit tests I wrote two months ago?

• Can I run all the unit tests I’ve written in no more than a few minutes?

• Can I run all the unit tests I’ve written at the push of a button?

• Can I write a basic unit test in no more than a few minutes?

Properties of a good unit test

• It should be automated and repeatable.• It should be easy to implement.• Once it’s written, it should remain for future

use.• Anyone should be able to run it.• It should run at the push of a button.• It should run quickly.

Styles of writing unit tests

• write production code first then unit tests;• test driven development(TDD): write the unit

tests first then production code;• behaviour driven development(BDD): start

from user stories and decompose them in scenarios then write code to validate the scenarios

Unit testing naming conventions used in examples

Object to be tested Object to create on the testing side

Project Create a test project named [ProjectUnderTest].Tests.

Class For each class, create at least one class with the name [ClassName]Tests.

Method For each method, create at least one test method with the following name:[MethodName]_[StateUnderTest]_[ExpectedBehavior].

Example 1 SimpleParserCustomTests

Unit testing framework - MsTest

• Automates unit testing;• Provides an intuitive easy to use interface;• Generates output that can be used by the

continuous integration process;• to write a unit test you just need to use

– two attributes [TestClass], [TestMethod];– a static function call Assert that validates the test;

Example 1SimpleParserTests

Unit testing classes that have dependencies

Example 2LegacyLogAnalyser

• Requirements:– create a class that analyses a log file;– if the log file is invalid call a webservice and log

the problem;– if an error is encountered send an email to an

administrator;

Controlling dependencies

• identify dependencies;• isolate them by introducing interfaces;• this process is referred to as making the class

under test testable;• during test replace interfaces with objects

that you can control(replace the dependency with a fake);

• this process is referred to as mocking the dependencies;

Example 2LogAnalyser

LogAnalyserTests

Mocking framework – Rhino.Mocks• a mocking framework facilitates the generation

of fakes;• there are two main types of unit testing;

– state-based unit testing;– interaction-based unit testing;

• there are two type of fakes to match the two types of unit testing: stub and mock;

• Rhino.Mocks is the most widely used open source framework;

• MockReposity.GenerateStub<T> and MockReposity.GenerateMock<T> are the methods used to generate fakes;

Example 2 LogAnalyserTestsWithRhinoMocks

Conclusion

• Defined the place of unit testing in the wider context of software testing;

• Defined properties of a good unit test;• Introduction to an unit testing framework;• Discussed about the need to isolate and

control dependencies during testing;• Introduction to a mocking framework.