test: add lazy_value test

CMakeLists.txt

@@ -608,6 +608,7 @@ if(WITH_TESTS)
     fragment_category_test
     incompressible_categorizer_test
     integral_value_parser_test
+    lazy_value_test
     metadata_requirements_test
     pcm_sample_transformer_test
     pcmaudio_categorizer_test

test/lazy_value_test.cpp

@@ -0,0 +1,42 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/**
+ * \author     Marcus Holland-Moritz (github@mhxnet.de)
+ * \copyright  Copyright (c) Marcus Holland-Moritz
+ *
+ * This file is part of dwarfs.
+ *
+ * dwarfs is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dwarfs is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dwarfs.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include "dwarfs/lazy_value.h"
+
+using namespace dwarfs;
+
+TEST(lazy_value_test, basic) {
+  int num_calls = 0;
+  lazy_value<int> v([&] {
+    ++num_calls;
+    return 42;
+  });
+  EXPECT_EQ(0, num_calls);
+  EXPECT_EQ(42, v.get());
+  EXPECT_EQ(1, num_calls);
+  EXPECT_EQ(42, v.get());
+  EXPECT_EQ(1, num_calls);
+  EXPECT_EQ(42, v());
+  EXPECT_EQ(1, num_calls);
+}