fixed backend tests

test/backends/ConnectionTest.cpp

@@ -8,13 +8,19 @@ using namespace matador::sql;
 
 TEST_CASE("Create connection test", "[connection]") {
   const connection c(matador::test::connection::dns);
-  REQUIRE(!c.is_open());
+  auto res = c.is_open();
+  REQUIRE(res);
+  REQUIRE(!*res);
 
   auto result = c.open();
   REQUIRE(result.is_ok());
-  REQUIRE(c.is_open());
+  res = c.is_open();
+  REQUIRE(res);
+  REQUIRE(*res);
 
   result = c.close();
   REQUIRE(result.is_ok());
-  REQUIRE(!c.is_open());
+  res = c.is_open();
+  REQUIRE(res);
+  REQUIRE(!*res);
 }