feat(cmake): Add JUNIT_OUTPUT_DIR option to doctest_discover_tests (#417)

Co-authored-by: Dennis Hezel <dh@3yourmind.com>
diff --git a/scripts/cmake/doctest.cmake b/scripts/cmake/doctest.cmake
index 1376801..8b81c9d 100644
--- a/scripts/cmake/doctest.cmake
+++ b/scripts/cmake/doctest.cmake
@@ -33,6 +33,7 @@
                          [TEST_SUFFIX suffix]
                          [PROPERTIES name1 value1...]
                          [TEST_LIST var]
+                         [JUNIT_OUTPUT_DIR dir]
     )
 
   ``doctest_discover_tests`` sets up a post-build command on the test executable
@@ -90,6 +91,13 @@
     executable is being used in multiple calls to ``doctest_discover_tests()``.
     Note that this variable is only available in CTest.
 
+  ``JUNIT_OUTPUT_DIR dir``
+    If specified, the parameter is passed along with ``--reporters=junit``
+    and ``--out=`` to the test executable. The actual file name is the same
+    as the test target, including prefix and suffix. This should be used
+    instead of EXTRA_ARGS to avoid race conditions writing the XML result
+    output when using parallel test execution.
+
 #]=======================================================================]
 
 #------------------------------------------------------------------------------
@@ -97,7 +105,7 @@
   cmake_parse_arguments(
     ""
     ""
-    "TEST_PREFIX;TEST_SUFFIX;WORKING_DIRECTORY;TEST_LIST"
+    "TEST_PREFIX;TEST_SUFFIX;WORKING_DIRECTORY;TEST_LIST;JUNIT_OUTPUT_DIR"
     "TEST_SPEC;EXTRA_ARGS;PROPERTIES"
     ${ARGN}
   )
@@ -134,6 +142,7 @@
             -D "TEST_PREFIX=${_TEST_PREFIX}"
             -D "TEST_SUFFIX=${_TEST_SUFFIX}"
             -D "TEST_LIST=${_TEST_LIST}"
+            -D "TEST_JUNIT_OUTPUT_DIR=${_JUNIT_OUTPUT_DIR}"
             -D "CTEST_FILE=${ctest_tests_file}"
             -P "${_DOCTEST_DISCOVER_TESTS_SCRIPT}"
     VERBATIM