An XML-formatted unit test results file that can be created by Microsoft Visual Studio or by the MSTest.exe. This file records the results of unit tests that are previously programmed to be run inside of Visual Studio or by the MSTest.exe command-line program.

Running either the Unit Test software in Microsoft Visual Studio or MSTest.exe will result in the creation of the TRX file, but in the case of Visual Studio, the results actually remain in memory until they are explicitly exported.