tests: Add a test that verifies absence of file leaks

If an out of memory error happens in load_file there's a danger of leaking
the FILE object. Since there is a limited supply of the objects we can easily
test that the leak does not happen.

tests/test_document.cpp

@@ -302,11 +302,33 @@ TEST(document_load_file_error)
 	pugi::xml_document doc;
 
 	CHECK(doc.load_file("filedoesnotexist").status == status_file_not_found);
+}
 
+TEST(document_load_file_out_of_memory)
+{
 	test_runner::_memory_fail_threshold = 1;
+
+	pugi::xml_document doc;
 	CHECK_ALLOC_FAIL(CHECK(doc.load_file("tests/data/small.xml").status == status_out_of_memory));
 }
 
+TEST(document_load_file_out_of_memory_file_leak)
+{
+	test_runner::_memory_fail_threshold = 1;
+
+	pugi::xml_document doc;
+
+	for (int i = 0; i < 256; ++i)
+	{
+		CHECK_ALLOC_FAIL(CHECK(doc.load_file("tests/data/small.xml").status == status_out_of_memory));
+	}
+
+	test_runner::_memory_fail_threshold = 0;
+
+	CHECK(doc.load_file("tests/data/small.xml"));
+	CHECK_NODE(doc, STR("<node />"));
+}
+
 TEST(document_load_file_error_previous)
 {
 	pugi::xml_document doc;