[test][python] allow to overwrite the interpreter for python test command

When using dune_python_add_test the SCRIPT is executed by default with the detected python interpreter. The optional INTERPRETER parameter allows to overwrite this setting, e.g. to pass additional command line arguments or to execute the tests using pytest.

cmake/modules/DunePythonTestCommand.cmake

@@ -4,15 +4,30 @@
 #
 #    .. cmake_param:: SCRIPT
 #       :multi:
-#       :required:
 #
 #       The script to execute using the python interpreter. It will be executed during :code:`make test_python`
-#       and during `ctest`.
+#       and during `ctest`. You are required to either pass SCRIPT or MODULE.
 #
 #       .. note::
 #
-#          The script will be executed using
-#          :code:`${Python3_EXECUTABLE} SCRIPT`.
+#          The script will be executed using :code:`${Python3_EXECUTABLE} SCRIPT`. If the INTERPRETER
+#          option is given, that interpreter is used instead.
+#
+#    .. cmake_param:: MODULE
+#       :multi:
+#
+#       The Python module to be executed.  It will be executed during :code:`make test_python`
+#       and during `ctest`. You are required to either pass SCRIPT or MODULE.
+#
+#       .. note::
+#
+#          The script will be executed using :code:`${Python3_EXECUTABLE} -m MODULE`. If the INTERPRETER
+#          option is given, that interpreter is used instead.
+#
+#    .. cmake_param:: INTERPRETER
+#       :single:
+#
+#       The Python interpreter to use for this test. It defaults to the one found by CMake.
 #
 #    .. cmake_param:: WORKING_DIRECTORY
 #       :single:
@@ -36,9 +51,9 @@ function(dune_python_add_test)
   # Parse Arguments
   include(CMakeParseArguments)
   set(OPTION)
-  set(SINGLE WORKING_DIRECTORY NAME)
-  set(MULTI SCRIPT COMMAND LABELS)
-  # set(MULTI COMMAND LABELS)
+  set(SINGLE WORKING_DIRECTORY NAME INTERPRETER)
+  set(MULTI SCRIPT COMMAND LABELS MODULE)
+
   cmake_parse_arguments(PYTEST "${OPTION}" "${SINGLE}" "${MULTI}" ${ARGN})
   if(PYTEST_COMMAND)
     message(FATAL_ERROR "dune_python_add_test: COMMAND argument should not be used, use SCRIPT instead providing only the Python script and not the Python interpreter")
@@ -48,11 +63,20 @@ function(dune_python_add_test)
   endif()
 
   # Apply defaults
+  if(NOT PYTEST_INTERPRETER)
+    set(PYTEST_INTERPRETER ${Python3_EXECUTABLE})
+  endif()
   if(NOT PYTEST_WORKING_DIRECTORY)
     set(PYTEST_WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
   endif()
-  if(NOT PYTEST_SCRIPT)
-    message(FATAL_ERROR "dune_python_add_test: no SCRIPT to execute specified!")
+  if((NOT PYTEST_MODULE) AND (NOT PYTEST_SCRIPT))
+    message(FATAL_ERROR "dune_python_add_test: Either SCRIPT or MODULE need to be specified!")
+  endif()
+  if(PYTEST_MODULE AND PYTEST_SCRIPT)
+    message(FATAL_ERROR "dune_python_add_test: You can only specify either SCRIPT or MODULE, not both!")
+  endif()
+  if(PYTEST_MODULE)
+    set(PYTEST_SCRIPT -m ${PYTEST_MODULE})
   endif()
   if(NOT PYTEST_NAME)
     set(commandstr "")
@@ -65,7 +89,7 @@ function(dune_python_add_test)
 
   # Actually run the command
   add_custom_target(target_${PYTEST_NAME}
-                    COMMAND ${Python3_EXECUTABLE} ${PYTEST_SCRIPT}
+                    COMMAND ${PYTEST_INTERPRETER} ${PYTEST_SCRIPT}
                     WORKING_DIRECTORY ${PYTEST_WORKING_DIRECTORY})
 
   # Build this during make test_python
@@ -75,7 +99,7 @@ function(dune_python_add_test)
   dune_declare_test_label(LABELS ${PYTEST_LABELS})
   # Also build this during ctest
   _add_test(NAME ${PYTEST_NAME}
-            COMMAND ${Python3_EXECUTABLE} ${PYTEST_SCRIPT}
+            COMMAND ${PYTEST_INTERPRETER} ${PYTEST_SCRIPT}
             WORKING_DIRECTORY ${PYTEST_WORKING_DIRECTORY}
             )
   # Set the labels on the test