diff --git a/src/numbers/numbers_test.go b/src/numbers/numbers_test.go
index a50f5e2..57ed479 100644
--- a/src/numbers/numbers_test.go
+++ b/src/numbers/numbers_test.go
@@ -1,9 +1,12 @@
 package main
 
 import (
+	"encoding/json"
+	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"testing"
+	"time"
 )
 
 // Tests valid and invalid URLs via 'validateURL'.
@@ -109,4 +112,110 @@ func TestHandler(t *testing.T) {
 			t.Errorf("Body not as expected, got %s, expected %s", body, expected)
 		}
 	}
+
+	// valid numbers, all in time
+	{
+		ts1 := httptest.NewServer(http.HandlerFunc(numbersHandlerInTime([]int{2, 3, 5, 7, 11, 13}, 0)))
+		defer ts1.Close()
+		ts2 := httptest.NewServer(http.HandlerFunc(numbersHandlerInTime([]int{1, 1, 2, 3, 5, 8, 13, 21}, 0)))
+		defer ts2.Close()
+		ts3 := httptest.NewServer(http.HandlerFunc(numbersHandlerInTime([]int{1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23}, 0)))
+		defer ts3.Close()
+		ts4 := httptest.NewServer(http.HandlerFunc(numbersHandlerInTime([]int{5, 17, 3, 19, 76, 24, 1, 5, 10, 34, 8, 27, 7}, 0)))
+		defer ts4.Close()
+
+		req, err := http.NewRequest("GET", fmt.Sprintf("/numbers?u=%s&u=%s&u=%s&u=%s", ts1.URL, ts2.URL, ts3.URL, ts4.URL), nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		rr := httptest.NewRecorder()
+		handler := http.HandlerFunc(numbersHandler)
+		handler.ServeHTTP(rr, req)
+
+		if status := rr.Code; status != http.StatusOK {
+			t.Errorf("Handler returned status code %v, expected %v", status, http.StatusOK)
+		}
+		body := rr.Body.String()
+		expected := "{\"Numbers\":[1,2,3,5,7,8,9,10,11,13,15,17,19,21,23,24,27,34,76]}\n"
+		if body != expected {
+			t.Errorf("Body not as expected, got %s, expected %s", body, expected)
+		}
+	}
+
+	// valid numbers, skipping those that are not in time or respond with "service unavailable"
+	{
+		ts1 := httptest.NewServer(http.HandlerFunc(numbersHandlerInTime([]int{2, 3, 5, 7, 11, 13}, 200)))
+		defer ts1.Close()
+		ts2 := httptest.NewServer(http.HandlerFunc(numbersHandlerInTime([]int{1, 1, 2, 3, 5, 8, 13, 21}, 300)))
+		defer ts2.Close()
+		ts3 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			http.Error(w, "service unavailable", http.StatusServiceUnavailable)
+		}))
+		defer ts3.Close()
+		ts4 := httptest.NewServer(http.HandlerFunc(numbersHandlerInTime([]int{5, 17, 3, 19, 76, 24, 1, 5, 10, 34, 8, 27, 7}, 500)))
+		defer ts4.Close()
+
+		req, err := http.NewRequest("GET", fmt.Sprintf("/numbers?u=%s&u=%s&u=%s&u=%s", ts1.URL, ts2.URL, ts3.URL, ts4.URL), nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		rr := httptest.NewRecorder()
+		handler := http.HandlerFunc(numbersHandler)
+		handler.ServeHTTP(rr, req)
+
+		if status := rr.Code; status != http.StatusOK {
+			t.Errorf("Handler returned status code %v, expected %v", status, http.StatusOK)
+		}
+		body := rr.Body.String()
+		expected := "{\"Numbers\":[1,2,3,5,7,8,11,13,21]}\n"
+		if body != expected {
+			t.Errorf("Body not as expected, got %s, expected %s", body, expected)
+		}
+	}
+
+	// ensure response time is below 500ms
+	{
+		ts := httptest.NewServer(http.HandlerFunc(numbersHandlerInTime([]int{5, 17, 3, 19, 76, 24, 1, 5, 10, 34, 8, 27, 7}, 500)))
+		defer ts.Close()
+
+		req, err := http.NewRequest("GET", fmt.Sprintf("/numbers?u=%s", ts.URL), nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		rr := httptest.NewRecorder()
+		handler := http.HandlerFunc(numbersHandler)
+		start := time.Now()
+		handler.ServeHTTP(rr, req)
+		end := time.Now()
+		elapsed := end.Sub(start)
+		fmt.Println(elapsed)
+
+		if status := rr.Code; status != http.StatusOK {
+			t.Errorf("Handler returned status code %v, expected %v", status, http.StatusOK)
+		}
+		body := rr.Body.String()
+		expected := "{\"Numbers\":[]}\n"
+		if body != expected {
+			t.Errorf("Body not as expected, got %s, expected %s", body, expected)
+		}
+
+		if elapsed > 500000000 {
+			t.Errorf("Time response not within 500ms, got %d", elapsed)
+		}
+	}
+
+}
+
+func numbersHandlerInTime(numbers []int, waitPeriod int) func(http.ResponseWriter, *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		time.Sleep(time.Duration(waitPeriod) * time.Millisecond)
+
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+
+		json.NewEncoder(w).Encode(map[string]interface{}{"Numbers": numbers})
+	}
 }