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Test Environment as a service (TEaaS, typically pronounced [teæs]), sometimes referred to as "on-demand test enviroment," is a test environment delivery model in which software and its associated data are hosted centrally (typically in the (Internet) cloud) and are typically accessed by users using a thin client, normally using a web browser over the Internet.

History
Centralized hosting of business application dates back to the 1960s. Starting at that decade, IBM and other mainframe providers conducted a service bureau business, often referred to as time-sharing or utility computing. Such services included offering computing power and database storage to banks and other large organizations from their worldwide data centers.

The expansion of the Internet during the 1990s brought about a new class of centralized computing, called Application Service Providers (ASP). Application service providers provided businesses with the service of hosting and managing specialized business applications, with the goal of reducing cost by central administration and through the solution provider's specialization in a particular business application.

Test Environment as a service is essentially an extension of the idea of the ASP model. The term Test Environment as a Service (TEaaS), however, is commonly used in more specific settings:
 * whereas most initial application service providers focused on managing and hosting third-party independent software vendors' software, contemporary TEaaS vendors typically develop and manage their own software;
 * whereas many initial application service providers offered more traditional client-server applications, which require installation of software on users' personal computers, contemporary software as a service solutions are predominantly web-based and only require an internet browser to use; and,
 * whereas the software architecture used by most initial application service providers mandated maintaining a separate instance of the application for each business, contemporary software as a service solutions normally utilize a multi-tenant architecture, in which the application is designed to serve multiple businesses and users, and partitions its data accordingly.

The TEaaS acronym is said to have first appeared in an article called "TEaaS: Test Environment as a Service", published in November 2010 in Professional Tester.

In November 2011 Manchester, UK based Digital Consultancy Intechnica launched CloudFlex a web application designed to make it easy to set up and manage test environments comprising virtual servers running on third-party cloud computing capacity. It provides a single environment used to manage server images, data, security, load balancing and geolocation.

Pricing
Unlike traditional software, conventionally sold as a perpetual license with an associated up-front fee (and, typically, smaller ongoing support fees), TEaaS providers generally price applications using a subscription fee, most commonly a monthly fee or an annual fee. Consequently, the initial setup cost for TEaaS is typically lower than the equivalent enterprise software. TEaaS vendors typically price their applications based on some usage parameters, such as the number of users ("seats") using the application. However, because in a TEaaS environment customers' data resides with the TEaaS vendor, opportunities also exist to charge per transaction, event, or other unit of value.

The relatively low cost for user provisioning (i.e., setting up a new customer) in a multi-tenant environment enables some TEaaS vendors to offer applications using the freemium model. In this model, a free service is made available with limited functionality or scope, and fees are charged for enhanced functionality or larger scope. Some other TEaaS applications are completely free to users, with revenue being derived from alternate sources such as advertising.

A key driver of TEaaS growth is TEaaS vendors' ability to provide a price that is competitive with on-premises software. This is consistent with the traditional rationale for outsourcing IT systems, which involves applying economies of scale to application operation, i.e., an outside service provider may be able offer better, cheaper, more reliable applications.

Architecture
The vast majority of TEaaS solutions are based on a multi-tenant architecture. With this model, a single version of the application, with a single configuration (hardware, network, operating system), is used for all customers ("tenants"). To support scalability, the application is installed on multiple machines (called horizontal scaling). In some cases, a second version of the application is set up to offer a select group of customers with access to pre-release versions of the applications (e.g., a beta version) for testing purposes. This is contrasted with traditional software, where multiple physical copies of the software—each potentially of a different version, with a potentially different configuration, and oftentimes customized—are installed across various customer sites.

Adoption drivers
With the Several important changes to the software market and technology landscape have facilitated acceptance and growth of TEaaS solutions:
 * The growing use of web-based user interfaces by applications, along with the proliferation of associated practices (e.g., web design), continuously decreased the need for traditional client-server applications. Consequently, traditional software vendors' investment in software based on fat clients has become a disadvantage (mandating ongoing support), opening the door for new software vendors offering a user experience perceived as more "modern".
 * The standardization of the web stack (HTML, JavaScript, CSS, HTTP), the increasing popularity of web development as a practice, and the introduction and ubiquitousness of web application frameworks gradually makes the instantiate, test and destroy model of a TEaaS solutions more attractive,
 * The increasing penetration of broadband Internet access enabled remote centrally-hosted applications to offer speed comparable to on-premises software.
 * The standardization of the HTTPS protocol as part of the web stack provided universally available lightweight security that is sufficient for most everyday applications.
 * The introduction and wide acceptance of lightweight integration protocols such as REST and SOAP enabled affordable integration between TEaaS applications (residing in the cloud) with internal applications over wide area networks and with other TEaaS applications.