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Mocking Web Services

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Some of the Web services testing approaches were previously covered in an InfoQ post. They have been recently extended through usage of Web Services mocking.

Mock objects are very popular and common approach to a unit testing. According to Wikipedia

mock objects are simulated objects that mimic the behavior of real objects in controlled ways… mock objects can simulate the behavior of complex, real (non-mock) objects and are therefore useful when a real object is difficult or impossible to incorporate into a unit test. If an object has any of the following characteristics, it may be useful to use a mock object in its place:
  • non-deterministic results (e.g. the current time or the current temperature);
  • has states that are difficult to create or reproduce (e.g. a network error);
  • is slow (e.g. a complete database, which would have to be initialized before the test);
  • does not yet exist or may change behavior;
  • would have to include information and methods exclusively for testing purposes (and not for its actual task)

Web services introduce additional situations where usage of mock approach can be very useful:

  • it is necessary to write a program that depends on one or more remote Web services, which can be running in production servers, and are not readily available in test servers, or third-party services that are running behind customer’s firewall and are not available for testing;
  • offline development, for example at home, or on the road, might require a full set of working Web services offline so that it is possible to test an implementation;
  • offline demos when the remote Web services might be not accessible and even not running all the time. It is necessary to make sure that the demo will behave properly in all of the above situations.

A new tutorial by Upul Godage describes how to use Apache Synapse to mock web services for development and testing. Apache Synapse is a simple, lightweight, high-performance enterprise service bus (ESB). Apache Synapse can be used to filter, transform, route, manipulate, and monitor SOAP, binary, XML, and plain text messages that can be delivered by HTTP, HTTPS, Java™ Message Service (JMS), Simple Mail Transfer Protocol (SMTP), Post Office Protocol Version 3 (POP3), FTP, file systems, and many other transport mediums.

Tutorial describes how Synapse can be used to define either fixed or controlled response from services using simple configuration XML files, defining transformation, building response for a given request (set of requests). It also describes approaches to mocking mediators using the same configurations – based approach.

Another approach to mocking of Web Services is usage of a newly released SOAPSimulator from Crosscheck Networks. Its functionality is similar to the one provided by Synapse, but with the following additional capabilities:

  • Graphical point and click SOAP and XML simulation.
  • Comprehensive WSDL and XSD schema support.
  • Dynamic WSDL and Schema retrieval from simulation instance.
  • Real-time simulation transaction monitoring.
  • WSDL and XSD report card to measure against corporate best practices.
  • Customizable runtime messaging governance analysis rules.
  • Multiple simultaneous service simulations.
  • Complex business logic simulation with runtime variable state machine.
  • WS-Security and WS-Identity extensibility.
  • Database and plug-in API extensibility.

Crosscheck Networks also provides a comprehensive tutorial on the product usage.

As defined in Accelerate your SOA Projects through Service Simulation white paper

Intense time pressures to build and deploy services leaves very little room for error in meeting business goals set forth for SOA projects. With IT budgets under constant pressure, tight delivery deadlines, and the drive to integrate systems within and across trading partners, SOA projects need to introduce service simulation within their environments. Service simulation decouples consumers and producer dependencies and enables them to implement independently. Web Services mocking solutions provides a "reference system in-a-box" and eliminates the expense associated with building a full-scale replica of the production system for the benefit of developers.

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