You need at least 2 things to make a linked list work:
1) A pointer to the head of the list.
2) A link in each node of the list to the next node (where NULL means end of list).

You have neither. You declared a whole bunch of test_result structs or pointers (5 if I counted right), but none of them are acting as the Head pointer, and none are linked using the next pointer.

You need a head node:
struct test_result * Head = NULL;

When you allocate a node, you need to add to list (add to start, it’s easier):
struct test_result *node = malloc(sizeof(struct test_result));
node->next = Head; // add to front of list
Head = node; // Make node the start of list.

average_finder needs a loop. You need to loop over all the nodes:
struct test_result *node = Head;
while(node != NULL)
{
// do stuff with node
node = node->next;
}