CMakeTests: allow to call the check_cmake_test macro with a given file

This allows to generate a lot of simple files directly in the test tree instead
of having them all checked in.

Tests/CMakeTests/CheckCMakeTest.cmake

@@ -1,30 +1,35 @@
 get_filename_component(CMakeTests_SRC_DIR ${CMAKE_CURRENT_LIST_FILE} PATH)
+
+function(check_cmake_test_single prefix test testfile)
+  message(STATUS "Test ${prefix}-${test}...")
+  execute_process(
+    COMMAND ${CMAKE_COMMAND} -P "${testfile}"
+    WORKING_DIRECTORY "${CMakeTests_BIN_DIR}"
+    OUTPUT_VARIABLE stdout
+    ERROR_VARIABLE stderr
+    RESULT_VARIABLE result
+    )
+  string(REGEX REPLACE "\n" "\n out> " out " out> ${stdout}")
+  string(REGEX REPLACE "\n" "\n err> " err " err> ${stderr}")
+  if(NOT "${result}" STREQUAL "${${test}-RESULT}")
+    message(FATAL_ERROR
+      "Test ${test} result is [${result}], not [${${test}-RESULT}].\n"
+      "Test ${test} output:\n"
+      "${out}\n"
+      "${err}")
+  endif()
+  if(${test}-STDERR AND NOT "${err}" MATCHES "${${test}-STDERR}")
+    message(FATAL_ERROR
+      "Test ${test} stderr does not match\n  ${${test}-STDERR}\n"
+      "Test ${test} output:\n"
+      "${out}\n"
+      "${err}")
+  endif()
+endfunction()
+
 function(check_cmake_test prefix)
   get_filename_component(CMakeTests_BIN_DIR ${CMAKE_CURRENT_LIST_FILE} PATH)
   foreach(test ${ARGN})
-    message(STATUS "Test ${prefix}-${test}...")
-    execute_process(
-      COMMAND ${CMAKE_COMMAND} -P "${CMakeTests_SRC_DIR}/${prefix}-${test}.cmake"
-      WORKING_DIRECTORY "${CMakeTests_BIN_DIR}"
-      OUTPUT_VARIABLE stdout
-      ERROR_VARIABLE stderr
-      RESULT_VARIABLE result
-      )
-    string(REGEX REPLACE "\n" "\n out> " out " out> ${stdout}")
-    string(REGEX REPLACE "\n" "\n err> " err " err> ${stderr}")
-    if(NOT "${result}" STREQUAL "${${test}-RESULT}")
-      message(FATAL_ERROR
-        "Test ${test} result is [${result}], not [${${test}-RESULT}].\n"
-        "Test ${test} output:\n"
-        "${out}\n"
-        "${err}")
-    endif()
-    if(${test}-STDERR AND NOT "${err}" MATCHES "${${test}-STDERR}")
-      message(FATAL_ERROR
-        "Test ${test} stderr does not match\n  ${${test}-STDERR}\n"
-        "Test ${test} output:\n"
-        "${out}\n"
-        "${err}")
-    endif()
+    check_cmake_test_single("${prefix}" "${test}" "${CMakeTests_SRC_DIR}/${prefix}-${test}.cmake")
   endforeach()
 endfunction()