rand: add test for rand.uuid_v4()

vlib/rand/random_numbers_test.v

@@ -175,3 +175,15 @@ fn test_rand_f64_in_range() {
 		assert value < max
 	}
 }
+
+fn test_rand_uuid_v4() {
+	uuid1 := rand.uuid_v4()
+	uuid2 := rand.uuid_v4()
+	uuid3 := rand.uuid_v4()
+	assert uuid1 != uuid2    
+	assert uuid1 != uuid3
+	assert uuid2 != uuid3
+	assert uuid1.len == 36    
+	assert uuid2.len == 36    
+	assert uuid3.len == 36
+}