Add a dummy writter for writing to /dev/null

lib/test/test_H5Writer.cpp

@@ -0,0 +1,12 @@
+
+#include "../src/H5Writer.hpp"
+using namespace std;
+
+TEST(H5Writer, get_h5_writer)
+{
+    auto dummy_writer = get_h5_writer("/dev/null");
+    EXPECT_TRUE(dynamic_cast<DummyH5Writer*>(dummy_writer.get()));
+
+    auto real_writer = get_h5_writer("real_file.h5");
+    EXPECT_FALSE(dynamic_cast<DummyH5Writer*>(real_writer.get()));
+}