The art of software testing. Myers (2nd edition) (2004) (The art of software testing. Myers (2nd edition) (2004).pdf), страница 34

Thus, another term for this tier isthe Presentation tier or layer, so dubbed because it provides the visualcontent to the end user. The Web server can use static HyperTextMarkup Language (HTML) pages or Common Gateway Interface(CGI) scripts to create dynamic HTML, but most likely it uses acombination of static and dynamic pages.Tier 2, or the Business layer, houses the application server. Hereyou run the software that models your business processes.

The following lists some of the functionality associated with the businesslayer:••••Transaction processingUser authenticationData validationApplication loggingThe third tier focuses on storing and retrieving data from a datasource, typically a relational database management system (RDBMS).Another term for Tier 3 is the Data layer. This tier consists of a database infrastructure to communicate with the second tier. The interface into the Data layer is defined by the data model, which describeshow you want to store data. Sometimes several database servers makeup this tier.

You typically tune database systems in this layer to handle the high transaction rates encountered in an e-commerce site. Inaddition to a database server, some e-commerce sites may place anauthentication server in this layer. Most often, you use an LDAP(Lightweight Directory Application Protocol) server for this function.Testing ChallengesYou will face many challenges when designing and testing Internetbased applications due to the large number of elements you cannotcontrol and the number of interdependent components. AdequatelyTesting Internet Applications197testing your application requires that you make some assumptionsabout the environment that your customers use and how they use thesite.An Internet-based application has many failure points that youshould consider when designing a testing approach.

The followinglist provides some examples of the challenges associated with testingInternet-based applications:• Large and varied user base. The users of your Website possessdifferent skill sets, employ a variety of browsers, and usedifferent operating systems or devices. You can also expectyour customers to access your Website using a wide range ofconnection speeds.

Not everyone has T1 or broadbandInternet access.• Business environment. If you operate an e-commerce site, thenyou must consider issues such as calculating taxes, determiningshipping costs, completing financial transactions, and trackingcustomer profiles.• Locales. Users may reside in other countries, in which case youwill have internationalization issues such as language translation,time zone considerations, and currency conversion.• Testing environments.

To properly test your application, you willneed to duplicate the production environment. This meansyou should use Web servers, application servers, and databaseservers that are identical to the production equipment. For themost accurate testing results, the network infrastructure willhave to be duplicated as well. This includes routers, switches,and firewalls.• Security.

Because your site is open to the world, you mustprotect it from hackers. They can bring your Website to agrinding halt with denial-of-service (DoS) attacks or rip offyour customers’ credit card information.Even from this list, which could be expanded considerably as weinclude viewpoints from a wide variety of developers and businesses,you can see that configuring a testing environment provides one of198The Art of Software Testingthe most challenging aspects of e-commerce development. Testingapplications that process financial transactions requires the most effortand expense.

You must replicate all the components, both hardwareand software, used for the application to produce valid test results.Configuring such an environment is a costly endeavor. You willincur not only equipment costs, but labor costs as well. Most companies fail to include these expenses when creating a budget for theirapplications.

Those that do include it generally underestimate thetime and monetary requirements. In addition, the testing environment needs a maintenance plan to support application upgradeefforts.Another significant testing challenge you face is testing browsercompatibility. There are several different browsers on the markettoday, and each behaves differently.

Although standards exist forbrowser operation, most vendors enhance their browsers to try andattract a loyal user base. Unfortunately, this causes the browsers tooperate in a nonstandard way. We cover this topic in greater detaillater in this chapter.Although many challenges exist when testing Internet-basedapplications, you should narrow your testing efforts to specific areas.Table 9.1 identifies some of the most important testing areas that canhelp ensure that users have a positive experience on your Website.Because the first impression is the most important impression,some of your testing will focus on usability and human-factor concerns. This area concentrates on the look and feel of your application. Items such as fonts, colors, and graphics play a major role inwhether users accept or reject your application.System performance also influences a customer’s first impression.As mentioned earlier, Internet users want instant gratification.

Theywill not wait long for pages to load or transactions to complete. Literally, a few seconds’ delay can cause your customer to try anothersite. Poor performance may also cause customers to doubt the reliability of your site. Therefore, you should set performance goals anddesign tests that reveal problems that cause your site to miss the goals.Users demand that the transaction occur rapidly and accuratelywhen purchasing products or services from your site. They do not,Testing Internet Applications199Table 9.1Examples of Presentation, Business, and Data Tier TestingPresentation Tier• Ensure fonts are thesame across browsers.••••••••Business Tier• Check for propercalculation of sales taxand shipping charges.Check to make sure• Ensure documentedall links point toperformance rates arevalid files or Websites.met for response timesCheck graphics toand throughput rates.ensure they are the• Verify that transactionscorrect resolutioncomplete properly.and size.• Ensure failedSpell-check each page.transactions roll backAllow a copy editorcorrectly.to check grammar• Ensure data areand style.collected correctly.Check cursorpositioning whenpage loads to ensureit is in the correcttext box.Check to ensuredefault button isselected when thepage loads.••Data TierEnsure databaseoperations meetperformance goals.Verify data arestored correctlyand accurately.Verify that you canrecover usingcurrent backups.Test failover orredundancyoperations.and should not, tolerate inaccurate billings or shipping errors.

Probably worse than losing a customer is finding yourself liable for morethan the transaction amount if your application does not processfinancial transactions correctly.Your application will likely collect data to complete tasks such aspurchases or e-mail registrations. Therefore, you should ensure thatthe data you collect are valid. For example, make sure that phonenumbers, ID numbers, currencies, e-mail addresses, and credit card200The Art of Software Testingnumbers are the correct length and are properly formatted.

In addition, you should check the integrity of your data. Localization issuescan easily cause data corruption via truncation due to character-setissues.In the Internet environment, it is critical to keep the Website available for customer use. This requires that you develop and implement maintenance guidelines for all the supporting applications andservers. Items such as the Web server and RDBMS require a highlevel of management. You must monitor logs, system resources, andbackups to ensure that these critical items do not fail. As described inChapter 6, you want to maximize the mean time between failures(MTBF) and minimize the mean time to recovery (MTTR) for thesesystems.Finally, network connectivity provides another area in which tofocus your testing efforts.

At some point, you can count on networkconnectivity going down. The source of the failure might be theInternet itself, your service provider, or your internal network.Therefore, you need to create contingency plans for your applicationand infrastructure to respond gracefully when an outage occurs.Keeping with the theme of testing, you should design your tests tobreak your contingency plans.Testing StrategiesDeveloping a testing strategy for Internet-based applications requiresa solid understanding of each of the hardware and software components that make up the application.

As is critical to successful testingof standard applications, a specification document is needed todescribe the expected functionality and performance of your Website. Without this document, you cannot design the appropriate tests.You need to test components developed internally and those purchased from a third party. For the components developed in-houseyou should employ the tactics presented in earlier chapters.

Thisincludes creating unit/module tests and performing code reviews.Testing Internet Applications201You should integrate the components into your system only afterverifying that they meet the design specifications and functionalityoutlined in the specification document.If you purchase components, then you need to develop a series ofsystem tests to validate that the items perform correctly independently of your application. Do not rely on the vendor’s quality-controlprogram to detect errors in its components. Ideally, you should complete this task independently of your application testing. Integratethese components only once you determine that they performacceptably. Including a nonfunctional third-party component in yourarchitecture makes it difficult to interpret test results and identify thesource of errors. Generally, you will use black-box approaches forthird-party components because you rarely have access to the component internals.Testing Internet-based applications is best tackled with a divideand-conquer approach.