Add tests for loading the catalog

pglablib/catalog/PgDatabaseSizes.h

@@ -0,0 +1,25 @@
+#ifndef PGDATABASESIZES_H
+#define PGDATABASESIZES_H
+
+#include "Pgsql_Connection.h"
+#include <libpq-fe.h>
+#include <cstdint>
+#include <vector>
+
+class PgDatabaseSize {
+public:
+	Oid oid;
+	int64_t totalBytes;
+
+	PgDatabaseSize()
+		: oid(InvalidOid)
+		, totalBytes(-1)
+	{}
+};
+
+using PgDatabaseSizes = std::vector<PgDatabaseSize>;
+
+/// Returns the size of every database. The size is -1 when the current role has no CONNECT privilege.
+PgDatabaseSizes loadDatabaseSizes(Pgsql::Connection &connection);
+
+#endif // PGDATABASESIZES_H