# Running Unit Tests

Unit tests are small tests of individual “units” of code. They allow developers and users to check that specific parts of the code are behaving as expected. These tests differ from integration or validation tests, which test how different units of the code interact.

If you are building from source, you can run the unit tests yourself to verify the the specific behaviors in the tests. Unit tests can never be comprehensive; the unit tests may all pass even if there is a bug in the code.

## Compiling Unit Tests

Unit tests are only supported with meson builds. You must build from source to build the unit tests. They are not part of the pre-compiled executables. For more information, see Installation, and Build SU2 on Linux/MacOS.

In order to compile the unit tests, add the flag -Denable-tests=true to your meson configure call. Then, you can build and run the tests by calling ninja test.

## Running Tests

There are three ways to run the main unit tests:

1. meson test -C builddir, where builddir is the build directory.
2. ninja test -C builddir, where builddir is the build directory.
3. ./UnitTests/test_driver from the SU2 build directory.

If you have run ninja install, then the test_driver executable will also be located in the bin directory where you have installed SU2. The first option will call ninja, which will then run the test_driver executable. The second option will call the test_driver executable. The last option, manually running the test driver, gives the most flexibility. This help page will focus on the command-line options for that last option.

By default, Catch2 will only show the output from failing tests. To also see the output for failing tests, add the command line argument -s when running the test_driver manually.

The above discussion over-simplifies the test driver setup. There are actually three test drivers: test_driver, test_driver_AD, and test_driver_DD. These test drivers are built or run depending on the type of installation (e.g. direcdiff, autodiff). For the most common use-case, you will not have a directdiff or autodiff build and will only use test_driver. If you call meson_test or ninja test, the correct drivers will run automatically. For more on tests using algorithmic differentiation or direct differentiation, see the section “AD and Direct-differentiation tests” below.

### Selecting subsets of the tests

You can also filter tests in two ways. The most basic, top-level grouping is by test cases. You can see all the test cases by running:

./UnitTests/test_driver --list-tests


You can then select a test case by name. For example, if I want to run the test case “Volume Computation”, I would run:

./UnitTests/test_driver "Volume Computation"


Within each test case, the test sections form trees of arbitrary depth. Each branch can be selected with the -c or the --section command line argument. For example, if I want to run the test section “2D Edge” from the test case “Volume Computation”, I would run:

./UnitTests/test_driver "Volume Computation" -c "2D Edge"


Further sub-sections can be selected by chaining together multiple “-c” selections, e.g.

./UnitTests/test_driver "Volume Computation" -c "Section Name" -c "Subsection Name"


You can also filter tests by tags. To see all the available tags, run:

./UnitTests/test_driver --list-tags


To run tests matching a specific tag, write the tag name in square braces as an argument for the test driver. For example, if I want to run the tests with the tag “Dual Grid”, I would run:

./UnitTests/test_driver "[Dual Grid]"


If you want to run tests matching any of multiple tags, then include them all in the quotations, but keep the square brackets separate. For example:

./UnitTests/test_driver "[Primal Grid], [Dual Grid]"


There is also a fundamental difference between "[Primal Grid], [Dual Grid]" and "[Primal Grid][Dual Grid]". The first selects all test matching either “Primal Grid” or “Dual Grid”. The second selects all tests matching both “Primal Grid” and “Dual Grid”. If that’s confusing to you or you would like to know more, then please read Catch2’s documentation.

While the above discussion focused on the test_driver, there are also two additional test drivers for algorithmic differentiation (AD) and direct-differentiation (DD). Because these executables need to be linked to different libraries (normal vs AD vs DD libraries), each exists as a standalone executable. As an example, test_driver_AD will test the SU2 libraries compiled with AD support.

Depending on your installation, one or two of these test drivers may be missing. This is normal. SU2 will only install the test drivers that match the compilation type you requested. For example, neither test_driver_AD nor test_driver_DD will be compiled if you build SU2 with the default options -Denable-autodiff=false and -Denable-directdiff=false.

To run the test drivers manually, you can run any of the three options from the build directory. If you installed the program, these test drivers will also be found in the bin folder of your install directory:

./UnitTests/test_driver