Test: Add example test

test/test_hello_world.cc

@@ -0,0 +1,44 @@
+// This file is under GNU General Public License 3.0
+// see LICENSE.txt
+#include "hello_world.hh"
+#include <iostream>
+
+// 2 Reasons why this 'using namespace' is okay
+// 1. We cannot put main() in the namespace pEp,
+// 2. If we were to extract parts of this file into a header-extension (hxx) as a template function/class
+// we would be in the namespace pEp anyways.
+using namespace pEp;
+
+int main()
+{
+    std::cout << "Test Hello World" << std::endl;
+    {
+        std::cout << "Test non-template func" << std::endl;
+        std::string ret = HelloWorld::hello_world();
+        std::cout << ret << std::endl;
+        assert(ret == "hello world");
+    }
+
+    {
+        std::cout << "Test invoke generated template for std::string" << std::endl;
+        std::string ret = HelloWorld::hello_world("pEp");
+        std::cout << ret << std::endl;
+        assert(ret == "pEp");
+    }
+
+    {
+        std::cout << "Test specialization for int" << std::endl;
+        int ret = HelloWorld::hello_world(404);
+        std::cout << ret << std::endl;
+        assert(ret == 808);
+    }
+
+    {
+        std::cout << "Test specialization for double" << std::endl;
+        double ret = HelloWorld::hello_world(4.04);
+        std::cout << ret << std::endl;
+        assert(ret == 8.08);
+    }
+    std::cout << "All tests passed" << std::endl;
+    return 0;
+}