Reduce cmake test boilerplate

All instances of mujoco_test in the code base were followed by
a call to  target_link_libraries(<testname> fixture gmock).

As anyhow mujoco_test already was calling target_link_libraries
to some predefined list of targets (mujoco and gtest_main),
this PR adds to the list of default linked targets also fixture
and gmock, to reduce the boilerplate.

Furthermore, to completly remove the need for calling
target_link_libraries after a call to mujoco_test, this PR also
add to the mujoco_test macro the ADDITIONAL_LINK_LIBRARIES
argument, that can be used if a given test needs to link some
additional targets beside the default ones.

To permit to use these new features also for mujoco benchmarks,
this PR adds a MAIN_TARGET parameter to mujoco_test, to select
if gtest_main or another target is used to provide the main
entry point to the test executable.

test/CMakeLists.txt

@@ -17,10 +17,22 @@ set(MUJOCO_TEST_WORKING_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 
 include(GoogleTest)
 
+# This macro is used to add a C++ test to MuJoCo CMake build system
+#
+# The CMake targets linked by default with target_link_libraries are:
+#   mujoco fixture gmock
+#
+# The macro supports the following parameters:
+#   * PROPERTIES: multiple value parameter, its value is set as test properties
+#                 via the set_tests_properties(<test> PROPERTIES <argument>) function
+#   * ADDITIONAL_LINK_LIBRARIES: multiple value parameter, additional libraries linked
+#                                to the test via target_link_libraries
+#   * MAIN_TARGET: single value parameter, used to specify the target linked to the tests
+#                  that define the main entry poiny. If not indicated, gest_main is used
 macro(mujoco_test name)
   set(options)
-  set(oneValueArgs)
-  set(multiValueArgs PROPERTIES)
+  set(oneValueArgs MAIN_TARGET)
+  set(multiValueArgs PROPERTIES ADDITIONAL_LINK_LIBRARIES)
   cmake_parse_arguments(
     _ARGS
     "${options}"
@@ -30,7 +42,15 @@ macro(mujoco_test name)
   )
 
   add_executable(${name} ${name}.cc)
-  target_link_libraries(${name} gtest_main mujoco)
+  target_link_libraries(${name} mujoco fixture gmock)
+  if(_ARGS_MAIN_TARGET)
+    target_link_libraries(${name} ${_ARGS_MAIN_TARGET})
+  else()
+    target_link_libraries(${name} gtest_main)
+  endif()
+  if(_ARGS_ADDITIONAL_LINK_LIBRARIES)
+    target_link_libraries(${name} ${_ARGS_ADDITIONAL_LINK_LIBRARIES})
+  endif()
   target_include_directories(${name} PRIVATE ${MUJOCO_TEST_INCLUDE})
   set_target_properties(${name} PROPERTIES BUILD_RPATH ${CMAKE_LIBRARY_OUTPUT_DIRECTORY})
   # gtest_discover_tests is recommended over gtest_add_tests, but has some issues in Windows.
@@ -48,6 +68,7 @@ macro(mujoco_test name)
   if(_ARGS_PROPERTIES)
     set_tests_properties(${testList} PROPERTIES ${_ARGS_PROPERTIES})
   endif()
+
 endmacro()
 
 add_library(fixture STATIC fixture.h fixture.cc)
@@ -67,13 +88,10 @@ target_link_libraries(
 target_include_directories(fixture PRIVATE ${mujoco_SOURCE_DIR}/include gmock)
 
 mujoco_test(fixture_test)
-target_link_libraries(fixture_test fixture gmock)
 
 mujoco_test(header_test)
-target_link_libraries(header_test fixture gmock)
 
 mujoco_test(pipeline_test)
-target_link_libraries(pipeline_test fixture gmock)
 
 add_subdirectory(benchmark)
 add_subdirectory(engine)