Unit testing

The main goal of unit tests in GROMACS is to help developers while developing the code. They focus on testing functionality of a certain module or a group of closely related modules. They are designed for quick execution, such that they are easy to run after every change to check that nothing has been broken.

Finding, building and running

As described in Source code organization, src/gromacs/ is divided into modules, each corresponding to a subdirectory. If available, unit tests for that module can be found in a tests/ subdirectory under the top-level module directory. Typically, tests for code in file.h in the module is in a corresponding tests/file.cpp. Not all files have corresponding tests, as it may not make sense to test that individual file in isolation. Focus of the tests is on functionality exposed outside the module. Some of the tests, in particular for higher-level modules, are more like integration tests, and test the functionality of multiple modules. Shared code used to implement the tests is in src/external/googletest/ and src/testutils/ (see below).

The tests are built if BUILD_TESTING=ON (the default) and GMX_BUILD_UNITTESTS=ON (the default) in CMake. Each module produces a separate unit test binary (module-test) under bin/, which can execute all the tests for that module.

The tests can be executed in a few different ways:

• Build the test target (e.g., make test): This runs all the tests using CTest. This includes also the regression tests if CMake has been told where to find them (regression tests are not discussed further on this page). If some of the tests fail, this only prints basic summary information (only a pass/fail status for each test binary or regression test class). You can execute the failing test binaries individually to get more information on the failure. Note that make test does not rebuild the test binaries if you have changed the source code, so you need to separately run make or make tests. The latter only builds the test binaries and their dependencies.

• Build the check target (e.g., make check): This behaves the same as the test target, with a few extensions:

  1. Test binaries are rebuilt if they are outdated before the tests are run.

  2. If a test fails, the output of the test binary is shown.

  3. If unit tests and/or regression tests are not available, a message is printed.

• Directly executing a test binary. This provides the most useful output for diagnosing failures, and allows debugging test failures. The output identifies the individual test(s) that fail, and shows the results of all failing assertions. Some tests also add extra information to failing assertions to make it easier to identify the reason. It is possible to control which tests are run using command line options. Execute the binary with -h to get additional information.

When executed using CTest, the tests produce XML output in Testing/Temporary/, containing the result of each test as well as failure messages. This XML is used by GitLab CI for reporting the test status for individual tests. Note that if a test crashes or fails because of an assert or a gmx_fatal() call, no XML is produced for the binary, and CI does not report anything for the test binary. The actual error is only visible in the console output.

Unit testing framework

The tests are written using Google Test, which provides a framework for writing unit tests and compiling them into a test binary. Most of the command line options provided by the test binaries are implemented by Google Test. See the Google Test Primer for an introduction. Some tests also use Google Mock, which provides a framework for creating mock implementations of C++ classes. Both components are included in the source tree under src/external/googletest/, and are compiled as part of the unit test build.

src/testutils/ contains GROMACS-specific shared test code. This includes a few parts:

• CMake macros for declaring test binaries. These take care of providing the main() method for the test executables and initializing the other parts of the framework, so that the test code in modules can focus on the actual tests. This is the only part of the framework that you need to know to be able to write simple tests: you can use gmx_add_unit_test() in CMake to create your test binary and start writing the actual tests right away. See src/testutils/TestMacros.cmake and existing CMake code for examples how to use them.

• Generic test fixtures and helper classes. The C++ API is documented on Doxygen page for testutils. Functionality here includes locating test input files from the source directory and constructing temporary files, adding custom command line options to the test binary, some custom test assertions for better exception and floating-point handling, utilities for constructing command line argument arrays, and test fixtures for tests that need to test long strings for correctness and for tests that execute legacy code where stdin reading etc. cannot be easily mocked.

• Some classes and functions to support the above. This code is for internal use of the CMake machinery to build and set up the test binaries, and to customize Google Test to suit our environment.

• Simple framework for building tests that check the results against reference data that is generated by the same test code. This can be used if it is not easy to verify the results of the code with C/C++ code alone, but manual inspection of the results is manageable. The general approach is documented on the Doxygen page on using the reference data.

In addition to src/testutils/, some of the module test directories may provide reusable test code that is used in higher-level tests. For example, the src/gromacs/analysisdata/tests/ provides test fixtures, a mock implementation for gmx::IAnalysisDataModule, and some helper classes that are also used in src/gromacs/trajectoryanalysis/tests/. These cases are handled using CMake object libraries that are linked to all the test binaries that need them.

Getting started with new tests

To start working with new tests, you should first read the Google Test documentation to get a basic understanding of the testing framework, and read the above description to understand how the tests are organized in GROMACS. It is not necessary to understand all the details, but an overall understanding helps to get started.

Writing a basic test is straightforward, and you can look at existing tests for examples. The existing tests have a varying level of complexity, so here are some pointers to find tests that use certain functionality:

• src/gromacs/utility/tests/stringutil.cpp contains very simple tests for functions. These do not use any fancy functionality, only plain Google Test assertions. The only thing required for these tests is the TEST() macro and the block following it, plus headers required to make them compile.

• The same file contains also simple tests using the reference framework to check line wrapping (the tests for gmx::TextLineWrapper). The test fixture for these tests is in src/testutils/stringtest.h/.cpp. The string test fixture also demonstrates how to add a custom command line option to the test binary to influence the test execution.

• src/gromacs/selection/tests/ contains more complex use of the reference framework. This is the code the reference framework was originally written for. src/gromacs/selection/tests/selectioncollection.cpp is the main file to look at.

• For more complex tests that do not use the reference framework, but instead do more complex verification in code, you can look at src/gromacs/selection/tests/nbsearch.cpp.

• For complex tests with mock-up classes and the reference framework, you can look at src/gromacs/analysisdata/tests/.

Here are some things to keep in mind when working with the unit tests:

• Try to keep the execution time for the tests as short as possible, while covering the most important paths in the code under test. Generally, tests should take seconds instead of minutes to run, so that no one needs to hesitate before running the tests after they have done some changes. Long-running tests should go somewhere else than in the unit test set. Note that CI will run the tests in several build configuration and slow tests will significantly slow down the pipelines and can even cause them to timeout.

• Try to produce useful messages when a test assertion fails. The assertion message should tell what went wrong, with no need to run the test itself under a debugger (e.g., if the assertion is within a loop, and the loop index is relevant for understanding why the assertion fails, it should be included in the message). Even better if even a user can understand what goes wrong, but the main audience for the messages is the developer who caused the test to fail.