A regression test is a test that you perform on an existing application to ensure that it is still working as expected.

When you are using Iguana or Chameleon to transform messages, you can use the msgtransform tool to perform a regression test of your VMD file. By comparing the output of msgtransform with the output from a previous test, you can ensure that the output from your application has not changed unexpectedly.

In this tutorial, you will learn how to use msgtransform to perform a simple regression test. You will:

• Run msgtransform on an existing VMD file;
• Change the VMD file;
• Run msgtransform again, comparing the new output with the old output.

Before starting, download this msgtransform.vmd file that you will use to perform the steps in this section. Save the file in a directory called test.

	Whether your company is a large or small organization, performing regular regression tests will help ensure you have a quality assurance plan from the start of the project planning phase. Using sample messages from each of your customers, you can easily set up daily automated regression tests to ensure that each release of your application parses various HL7 flavors in the same fashion.