# Unit Testing¶

Unit testing is a standard software engineering practice to aid in ensuring a quality product. A good suite of unit tests provides confidence in refactoring and changing code, furnishes some documentation on how classes and functions are used, and can drive a more decoupled design.

If unit tests do not already exist for a section of code, you are encouraged to add them when modifying that section of code. New code additions should also include unit tests. When possible, fixes for specific bugs should also include a unit test that would have caught the bug.

## Unit testing framework¶

The Catch framework is used for unit testing. See the project site for a tutorial and documentation: https://github.com/philsquared/Catch.

Catch consists solely of header files. It is distributed as a single include file about 400 KB in size. In QMCPACK, it is stored in external_codes/catch.

## Unit test organization¶

The source for the unit tests is located in the tests directory under each directory in src (e.g., src/QMCWavefunctions/tests). All of the tests in each tests directory get compiled into an executable. After building the project, the individual unit test executables can be found in build/tests/bin. For example, the tests in src/QMCWavefunctions/tests are compiled into build/tests/bin/test_wavefunction.

All the unit test executables are collected under ctest with the unit label. When checking the whole code, it is useful to run through CMake (cmake -L unit). When working on an individual directory, it is useful to run the individual executable.

Some of the tests reference input files. The unit test CMake setup places those input files in particular locations under the tests directory (e.g., tests/xml_test). The individual test needs to be run from that directory to find the expected input files.

Command line options are available on the unit test executables. Some of the more useful ones are

• List command line options.

• List all the tests in the executable.

A test name can be given on the command line to execute just that test. This is useful when iterating on a particular test or when running in the debugger. Test names often contain spaces, so most command line environments require enclosing the test name in single or double quotes.

## Example¶

The first example is one test from src/Numerics/tests/test_grid_functor.cpp.

Listing 76 Unit test example using Catch.
TEST_CASE("double_1d_grid_functor", "[numerics]")
{
LinearGrid<double> grid;
OneDimGridFunctor<double> f(&grid);

grid.set(0.0, 1.0, 3);

REQUIRE(grid.size() == 3);
REQUIRE(grid.rmin() == 0.0);
REQUIRE(grid.rmax() == 1.0);
REQUIRE(grid.dh() == Approx(0.5));
REQUIRE(grid.dr(1) == Approx(0.5));
}


The test function declaration is TEST_CASE("double_1d_grid_functor","[numerics]"). The first argument is the test name, and it must be unique in the test suite. The second argument is an optional list of tags. Each tag is a name surrounded by brackets ("[tag1][tag2]"). It can also be the empty string.

The REQUIRE macro accepts expressions with C++ comparison operators and records an error if the value of the expression is false.

Floating point numbers may have small differences due to roundoff, etc. The Approx class adds some tolerance to the comparison. Place it on either side of the comparison (e.g., Approx(a) == 0.3 or a = Approx(0.3)). To adjust the tolerance, use the epsilon and scale methods to Approx (REQUIRE(Approx(a).epsilon(0.001) = 0.3);.

### Expected output¶

When running the test executables individually, the output of a run with no failures should look like

===============================================================================
All tests passed (26 assertions in 4 test cases)


A test with failures will look like

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test_numerics is a Catch v1.4.0 host application.
Run with -? for options

-------------------------------------------------------------------------------
double_1d_grid_functor
-------------------------------------------------------------------------------
/home/user/qmcpack/src/Numerics/tests/test_grid_functor.cpp:29
...............................................................................

/home/user/qmcpack/src/Numerics/tests/test_grid_functor.cpp:39: FAILED:
REQUIRE( grid.dh() == Approx(0.6) )
with expansion:
0.5 == Approx( 0.6 )

===============================================================================
test cases:  4 |  3 passed | 1 failed
assertions: 25 | 24 passed | 1 failed


Three scenarios are covered here: adding a new test in an existing file, adding a new test file, and adding a new test directory.

### Adding a test to existing file¶

Copy an existing test or from the example shown here. Be sure to change the test name.

When adding a new test file, create a file in the test directory, or copy from an existing file. Add the file name to the ADD_EXECUTABLE in the CMakeLists.txt file in that directory.

One (and only one) file must define the main function for the test executable by defining CATCH_CONFIG_MAIN before including the Catch header. If more than one file defines this value, there will be linking errors about multiply defined values.

Some of the tests need to shut down MPI properly to avoid extraneous error messages. Those tests include Message/catch_mpi_main.hpp instead of defining CATCH_CONFIG_MAIN.

Copy the CMakeLists.txt file from an existing tests directory. Change the SRC_DIR name and the files in the ADD_EXECUTABLES line. The libraries to link in TARGET_LINK_LIBRARIES may need to be updated.
Add the new test directory to src/CMakeLists.txt in the BUILD_UNIT_TESTS section near the end.
The Utilities directory contains a “fake” random number generator that can be used for deterministic tests of these parts of the code. Currently it outputs a single, fixed value every time it is called, but it could be expanded to produce more varied, but still deterministic, sequences. See src/QMCDrivers/test_vmc.cpp for an example of using the fake random number generator.