Adjust prerequisites for tests in cmake

CMakeLists.txt

@@ -73,8 +73,12 @@ ADD_CUSTOM_TARGET(apidoc
     WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
 
 if(ENABLE_TESTING)
+    find_package(PERL)
+
+    if(PERL_FOUND)
         add_subdirectory(tests)
 
+        if(UNIX)
             ADD_CUSTOM_TARGET(covtest
                 COMMAND make test
                 COMMAND programs/test/selftest
@@ -100,4 +104,6 @@ if(ENABLE_TESTING)
                 COMMAND rm -f memcheck.log
                 COMMAND mv DartConfiguration.tcl.bak DartConfiguration.tcl
             )
+        endif(UNIX)
+    endif(PERL_FOUND)
 endif()