Data Files for Testing


This page gives an overview of how data files are managed within Mantid.


Some unit tests use a small amount of data that is created by the test harness and others load data from a file. Take the example of ApplyCalibrationTest. In its first test, testSimple, it creates a workspace with 10 detectors using WorkspaceCreationHelper::create2DWorkspaceWithFullInstrument(). In the second test, testComplex, it reads a file IDFs_for_UNIT_TESTING/MAPS_Definition_Reduced.xml, which contains the definition of a MAPS instrument with the number of detectors reduced much to ensure it is read quickly but preserving the other properties of this instrument. However, new tests should avoid even loading of this nature unless there is a strong justification for doing so.

Main issues:

  • need to store data, mainly for testing, alongside the code
  • some data needs to be versioned
  • merging system tests back with main code requires handling large data files
  • git is bad at handling binary files

Possible solutions:

  • CMake’s ExternalData
  • don’t have any reference to data in git and force developers to manage the data stored on a file server
  • extensions to git, e.g. git-fat, git-annex to deal with large files

We have chosen to use CMake as it is already in use as a build system and it doesn’t involve introducing extra work with git.

CMake’s External Data


  • content - the real data
  • content link - text file containing a hash (MD5) of the real content. The filename is the filename of the real data plus the .md5 extension
  • object - a file that stores the real data and whose name is the MD5 hash of the content


  • git does not store any content, it only stores content links
  • content is stored on a remote server that can be accessed via a http link
  • running cmake sets up build rules so that the content is downloaded when dependent projects are built

Local Object Store

CMake does not download content directly but stores the content in a Local Object Store, whose location is defined by the ExternalData_OBJECT_STORES CMake variable. This allows it to share content between build trees, especially useful for continuous integration servers.

Binary Root

The final step is to create the real filename and symbolic link (copy on windows) it to the object in the local object store. The location of the real filenames is controlled by the ExternalData_BINARY_ROOT CMake variable and defaults to build/ExternalData.

Using Existing Data

There are two places files may be found:

Adding A New File(s)

A helper git command is defined called add-test-data. It would be called like this:

git add-test-data Testing/Data/UnitTest/INST12345.nxs

This does the following:

  • computes the MD5 hash of the data, e.g. d6948514d78db7fe251efb6cce4a9b83
  • stores the MD5 hash in a file called Testing/Data/UnitTest/INST12345.nxs.md5
  • renames the original data file to be its md5 sum Testing/Data/UnitTest/d6948514d78db7fe251efb6cce4a9b83
  • runs git add Testing/Data/UnitTest/INST12345.nxs.md5
  • tells the user to upload the file(s), d6948514d78db7fe251efb6cce4a9b83, to the remote store


  • For the change to have effect, re-run cmake in the build area
  • You need to use a shell to add & modify data files under Windows in this way. Not every shell works as described, though Github for Windows shell would allow you to do everything described here step by step without deviations. Unfortunately, MINGW32 shell you have to select to do that is not the most convenient shell under Windows. In addition to that, add-test-data script is currently broken (at least was on 20/11/2015) . This is why I would suggest to use small python script, provided below, which would calculate md5 hash, create the .md5 file and rename your test or reference file according to the hash sum calculated. You then have to manually put .md5 file to requested reference data location and add it to Git by usual means. The hash-sum named file should be, as in the case of Unix, placed to the remote store
  • Note, that ILL test data should be placed under ILL/${INSTRUMENT} subdirectories (e.g. ILL/IN16B), and should not contain any instrument prefix in the file name.

Updating File(s)

The workflow is the same as adding new files except that the developer must first put the new version of the file in the right place. For the example above, it would be Testing/Data/UnitTest/INST12345.nxs. Then the new .md5 file and associated renamed file will be created. git diff will show that change to the contents of Testing/Data/UnitTest/INST12345.nxs.md5 and that there is an untracked file with the md5 sum for a name.

Developer Setup

To add the add-test-data command alias to git run

git config alias.add-test-data '!bash -c "tools/Development/git/git-add-test-data $*"'

in the git bash shell (script source). The single quotes are important so that bash doesn’t expand the exclamation mark as a variable.

It is advised that CMake is told where to put the “real” data as the default is $HOME/MantidExternalData on Linux/Mac or C:/MantidExternalData on Windows. Over time the store will grow so it is recommended that it be placed on a disk with a large amount of space. CMake uses the MANTID_DATA_STORE variable to define where the data is stored.

Example cmake command:


mkdir -p build
cmake -DMANTID_DATA_STORE=/home/mgigg/Data/LocalObjectStore ../Code/Mantid


mkdir build
cmake -DMANTID_DATA_STORE=D:/Data/LocalObjectStore ../Code/Mantid

Setting With Dropbox:

This is for people in the ORNL dropbox share and has the effect of reducing external network traffic. There is a gist for getting dropbox running on linux. Instead of defining the MANTID_DATA_STORE in cmake, it is simplest to create a symbolic link

ln -s ~/Dropbox\ \(ORNL\)/MantidExternalData ~

Then everything will happen automatically using CMake’s default behavior.

Proxy Settings

If you are sitting behind a proxy server then the shell or Visual studio needs to know about the proxy server. You must set the http_proxy environment variable to http://HOSTNAME:PORT.

On Windows you go to Control Panel->System and Security->System->Advanced System settings->Environment Variables and click New... to add a variable.

On Linux/Mac you will need to set the variable in the shell profile or on Linux you can set it system wide in /etc/environment.


If you find that your tests cannot find the data they require check the following gotchas:

  • Check that you have re-run CMake in the build directory
  • Check that you have uploaded the original file renamed as a hash to the Mantid file repository
  • Check that you have removed any user defined data search directories in ~/.mantid
  • Check that you have rebuilt the test executable you’re trying to run
  • Check that you have rebuilt the SystemTestData target