Skip to main content

ITK3 Test Harness - user guidance

Published 31 July 2018

This document explains the steps to gain credentials for the use of the ITK3 Test Harness. It also gives some information relating to functionality of the software.


The NHS Digital Interoperability Standards Service has developed a set of generic Fast Healthcare Interoperability Resources (FHIR) messaging components to allow a standardised approach to using FHIR message headers and responses across NHS message and document flows in England. These components, along with NHS Digital FHIR message and FHIR document specifications, are part of the ITK3 solution.

View the message specification and implementation guide

View specifications describing a specific payload, in this case Transfer of Care, that could be carried by the ITK3 FHIR messaging components

FHIR messages will be sent using Message Exchange for Social Care and Health (MESH) from sender to recipient as per the ITK3 specifications. To ensure that senders are clear on the successful receipt or otherwise of their messages, a piece of software, a Test Harness, has been built to produce standard
responses, including failures of messages.

Standard error codes and descriptions will be returned depending on the nature of the success/failure of a message. View details of expected response codes

The ITK3 Test Harness simulates the expected response of a receiving primary care practice system and the behaviour of a hospital sending system. The ITK3 Test Harness is situated within the NHS Digital Opentest environment, which is accessible via open source virtual private network (OpenVPN).

The transport mechanism used is MESH.

More detailed information about the ITK3 Test Harness


This document is intended for ITK3 message specification implementers who wish to access the ITK3 Test Harness to confirm the validity of their messages and to check that the various responses returned by the ITK3 can be correctly catered for.

Process for accessing the ITK3 Test Harness

There are several prerequisites for use of the ITK3 Test harness via a local MESH client:

  1. Access to Opentest Environment.
  2. Ownership of a MESH mailbox within Opentest.
  3. A local MESH Client installation configured for the Opentest environment.

To fulfil any of the above prerequisites, potential users should send an email to to register their interest and their contact details  would be verified with the relevant NHS Digital programme.

Users may also wish to:

  • receive test harness validation reports
  • gain access to the Opentest portal to view validation reports and logs

These can be obtained by additionally supplying an email address to register.

It is also possible to access the software via a MESH API. If this is required, please email in the first instance.

On receipt of the email, NHS Digital will:

  1. Request Opentest access on the supplier’s behalf through the NHS Digital Solution Assurance Service Desk.
  2. Request MESH mailboxes for a new or existing Opentest connection through the NHS Digital Solution Assurance Service Desk.
  3. Confirm and configure the requested supplier email address to receive validation reports, if required.
  4. Provide support, if necessary, on post-configuration of MESH client to access Opentest.
  5. Create supplier specific Opentest portal credentials, if required.

Additional support with messages to the ITK3 Test Harness

Users may require additional support constructing messages, such as:

  • XML valid messages
  • messages which conform to the NHS Digital message specifications

There are several validation tools available which support implementers in creating valid and profile conformant messages.

The FHIR website has a section concerning validation; a variety of validation tools for general use can be downloaded from this area.

Additional validation tools can be obtained from the FHIR community, including clarotech.

Guidance to creating valid and conformant messages is available by emailing

Last edited: 12 July 2019 11:01 am