diff --git a/test_map_hash_key.c b/test_map_hash_key.c
index 9ffcf57..c90651c 100644
--- a/test_map_hash_key.c
+++ b/test_map_hash_key.c
@@ -1,17 +1,36 @@
+#include <stdbool.h>
+
 #include <criterion/criterion.h>
 #include "cig.h"
 
-#define KEYS_LEN 100
+typedef long long T;
+#define CAPACITY 50
 
 Test(map_hash_key, foo) {
 	map_header_t header = (map_header_t){0};
-	long long key_hashes[KEYS_LEN];
+	header.key_size = sizeof(T);
+	header.mapping_capacity = CAPACITY;
 
-	for (long long i = 0; i < KEYS_LEN; i++) {
-		header.key_size = sizeof(i);
-		key_hashes[i] = map_hash_key(&header, (const uint8_t*)(&i));
-		// TODO
+	bool hashed[CAPACITY] = {0};
+
+	for (T i = 0; i < CAPACITY; i++) {
+		uint32_t index = map_hash_key(&header, (const uint8_t*)(&i));
+		cr_assert(index < CAPACITY);
+		hashed[index] = true;
 	}
-	
-	map_hash_key(&header)
+
+	int n_unique = 0;
+
+	for (int i = 0; i < CAPACITY; i++) {
+		if (hashed[i]) {
+			n_unique++;
+		}
+	}
+
+	cr_assert_gt(n_unique, 1);
+	cr_assert_lt(n_unique, CAPACITY);
+
+	printf("Expect high number below 50. Got %d unique hashes.\nThis means %d collisions\n", n_unique, (int)(CAPACITY - n_unique));
 }
+
+// TODO: test hash with custom hash function.