Add utility function to test lib to create a test directory

There is an identical function in libardour test support lib so we
should probably find a better place to put this at some point

libs/pbd/test/test_common.cc

@@ -16,9 +16,14 @@
     675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
+#include "test_common.h"
+
+#include <glibmm/fileutils.h>
 #include <glibmm/miscutils.h>
 
-#include "test_common.h"
+#include <sstream>
+
+using namespace std;
 
 /**
  * This allows tests to find the data files they require by looking
@@ -35,3 +40,20 @@ test_search_path ()
 	return Glib::getenv("PBD_TEST_PATH");
 #endif
 }
+
+std::string
+test_output_directory (std::string prefix)
+{
+	std::string tmp_dir = Glib::build_filename (g_get_tmp_dir(), "pbd_test");
+	std::string dir_name;
+	std::string new_test_dir;
+	do {
+		ostringstream oss;
+		oss << prefix;
+		oss << g_random_int ();
+		dir_name = oss.str();
+		new_test_dir = Glib::build_filename (tmp_dir, dir_name);
+		if (Glib::file_test (new_test_dir, Glib::FILE_TEST_EXISTS)) continue;
+	} while (g_mkdir_with_parents (new_test_dir.c_str(), 0755) != 0);
+	return new_test_dir;
+}

libs/pbd/test/test_common.h

@@ -23,4 +23,6 @@
 
 PBD::Searchpath test_search_path ();
 
+std::string test_output_directory (std::string prefix);
+
 #endif