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Tài liệu Java Testing and Design- P5 pdf
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What Usually Goes Wrong 179
If the browser ignores cache-defeating tags, then your best strategy is to
create dynamic Web content that users can use to tell they are viewing cached
pages. For example, if every page contains an incrementing simple integer
number, then refreshing a page should increment the serial number. A page
with the same number indicates the user is viewing a cached page. Additionally, the test can check the date/time values in the HTTP response header.
Invalid Data
Browsers make GET and POST requests to the server using HTTP protocols.
The GET request includes a URL, HTTP header information, and a series of
name/value pairs. For example, imagine a Web page that offers a list of movies. Each movie name appears as a hyperlink for the user to click. When the
user clicks a link, the browser sends a GET request to the server:
GET /signin_handler?name=frank&movie=Star%20Wars HTTP/1.0
User-Agent: Mozilla 5.28
Host: examples.pushtotest.com
Accept: text/html, image/gif, image/jpeg, *;
Connection: keep-alive
While the HTTP GET command is very lightweight and universally used, it
does little to tell the server about the identity of the data. How does the server
know that there will be both a name and movie value? How does it know a
valid movie value from an invalid one? Or that the movie value is URL
encoded? The browser may construct what it thinks is a perfectly valid GET
request, but the server may disagree. Software test strategies for validating
data are essential to deploying high-quality HTTP/HTML Web applications.
To catch most problems, you should search for each of the following types
of invalid data each time you test a Web-enabled application:
• Too few or too many parameters—HTTP/HTML
environments have no defined specification of the parameters
that will be sent or received. It is up to the developer and
HTML designer to agree prior to building the application.
Testing a Web-enabled application by sending less than the
expected number of parameters will usually turn up broken
server logic and security holes.
• Wrongly ordered data—Ordering tests for the proper
sequence of the occurrence of data. For example, an ordering
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180 Chapter 6 Design and Test in HTTP/HTML Environments
test would send a bank account transfer command to a server
without first issuing a GET command that identifies the back
account number in the server session. The test learns how the
server handles an out-of-order situation.
• Boundary data errors—Range tests the validity of the values.
If a name may be no longer than 15 characters, a test
determines how the server handles a 17-character-long name.
• Wrongly formatted data—There is no schema to define the
contents of data in HTTP/HTML environments. Every piece of
data is a string of characters. There is also no definition of a
character. The HTTP header values in the call may optionally
contain a definition of the encoding type (UTF-8), for example.
Let’s look at an example of wrongly formatted data in more depth. HTTP/
HTML Web applications are particularly vulnerable to invalid data problems
because of the nature of HTML. HTML mixes the instructions to lay out a
page with the content that appears in the page. Even today popular tools for
HTML editing can easily create invalid HTML codes. Special tests must be
created to see how the server responds when it receives an invalid HTML
form. For example, the following HTML is missing a closing double-quote
character in the first input tag:
<html>
<body>
<form action="signin_handler">
<input name="signin_name value="Default user">
<input name="password" type="password" value="pass">
</form>
</body>
</html>
The server receives a POST command that looks like this:
POST /signin_handler HTTP/1.1
Referrer: http://examples.pushtotest.com/...
Content-length: 178
signin_name%2Fvalue=&password=pass
Note the signin_name%2Fvalue= parameter, which is caused by the
missing double quote character. Seeing how the server responds to this kind
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What Usually Goes Wrong 181
of invalid data is mandatory for a successful test strategy, especially in HTTP/
HTML Web applications.
Session Problems
The original design for HTTP/HTML environments was stateless. Each
request and response stood alone. Dynamic and personalized Web applications implement state using Cookies, Applets, ActiveX controls, and specially
coded URLs. Each time stateful information is introduced, the server needs
to record the state data in a session. Intelligent test agents are particularly
well suited to test a Web-enabled application for session problems.
Intelligent test agents implement these session tests with ease:
• Invalid session identities—Each Web-enabled application
formats session identifiers according to its own scheme. For
example, the Cookie value for the PushToTest Web site looks like
this: 38849198981. Each new user at a unique IP address bumps
up the number by 1. A test agent should try valid numbers such
as those received from the server. But it should also invent
session identifiers to see how the server handles the invalid data.
• Long sessions—Each session requires the server to use
resources to store session data. The Web-enabled application
recycles its resources as sessions end. Test agents may easily
push the server resources to maximum by continuing to use the
same session information for a long period of time.
As we have seen, many things can and do go wrong in an HTTP/HTML
Web application. Constructing and running HTTP test agents is a good technique to find and solve these problems.
Constructing HTTP Test Agents
In this section, we explore constructing HTTP test agent scripts. To get handson I will present a complete test script that you can run in TestMaker. Chapter
5 first introduced TestMaker. First I describe the outline of an intelligent test
agent and show how the agent script makes requests to the server, validates
cookies, sessions, and redirection, and validates the server responses.
The central theme in intelligent test agent technology is to learn a system’s
scalability, performance, and functional characteristics before customers are
exposed to bugs, failures, and scalability problems. Intelligent test agents
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182 Chapter 6 Design and Test in HTTP/HTML Environments
emulate a user archetype, as in the case of the plodding, slow, and easily distracted Wanderer agent described in the next section. Figure 6–3 shows how
the Wanderer is typical of an intelligent test agent that runs concurrently
with other agents to simulate a near real-world environment where a server
handles many users concurrently. The other concurrently running agents
emulate their own user archetypes: The Validator randomly reads and checks
the content of Web pages and the Sign-In Agent tries to sign in to a Webenabled application using a variety of user names and passwords.
The Wanderer is an intelligent test agent that randomly reads pages on a
test server hosted by PushToTest, the principal maintainers of TestMaker.
The Wanderer initially uses an HTTPProtocol object to get a Web page. It
then finds hyperlinks on that page and follows a random hyperlink. The Wanderer also keeps track of the time it takes to receive each page. Just for fun
the Wanderer pauses after every tenth-loaded Web page and gives an award
to the Web page that took the longest time to load.
TestMaker comes with everything needed to create and run the Wanderer,
Sign-In, and Validator intelligent test agents. While TestMaker’s New Agent
Wizard automatically creates intelligent test agents using an easy-to-use
graphical user interface, understanding TestMaker’s components is important to successfully writing and running your own intelligent test agents (see
Figure 6–4).
While Chapter 5 introduced TestMaker, it is important at this point to show
how TestMaker’s components fit into one another. TestMaker defines the
TOOL to provide a common interface to an extensible set of protocol handlers to communicate with servers using HTTP, HTTPS, SOAP, and XMLRPC protocols. TestMaker comes with JDOM, a utility for working with XML
data that we will see used by the Validator agent later in this chapter.
Figure 6–3 Shows an HTTP/HTML Web-enabled application being tested by
multiple, concurrently running intelligent test agents.
Sign-In Agent
The Wanderer The Validator
HTTP/HTML
Web Service
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What Usually Goes Wrong 183
The Jython scripting language is the glue between your test agent and the
TOOL objects. To assist you, TestMaker comes with a Recorder that looks at
HTML pages and writes the Jython scripts needed to test an HTTP/HTML
Web-enabled application.
TOOL implements an HTTPProtocol object you can use for HTTP and
HTTPS (secure) protocols, to issue GET and POST requests, to handle HTTP
header parameters (including Cookies), and to search the server response.
Figure 6–5 shows an overview of the HTTPProtocol object.
Figure 6–4 An architectural view of the TestMaker environment showing all the
components provided to build intelligent test agents.
Figure 6–5 TOOL’s HTTPProtocol object contains objects to connect to an
identified host over HTTP and HTTPS protocols, to pass parameters, and to search
the results.
TestMaker
Graphical environment for writing and
running intelligent test agents
Jython
Scripting, Threads, Expressions,
Functions, Variables, Conditions
TOOL
Protocol Handlers: HTTP, SOAP, etc.
Utilities
JDOM for XML parsing
Your Java Objects
HTTPProtocol
HTTPHeader
Parameters
HTTPBody
SimpleSearch
Request Parameters
ResponseLink
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