✨ (concurrency-and-select): add basic test

Author: yuanyu90221

select/README.md

@@ -0,0 +1,7 @@
+# select
+
+當遇到多個 goroutine 需要溝通時，可以透過 channel 來傳遞資料
+而當遇到多個資料需要傳遞給一個 goroutine 時
+
+這時可以透過 select 語法來最有效的等候多個 channel 的傳遞資訊
+

select/select.go

@@ -0,0 +1,39 @@
+package select_sample
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+)
+
+var tenSecondTimeout = 10 * time.Second
+
+func ConfigurableRacer(a, b string, timeout time.Duration) (winner string, error error) {
+	select {
+	case <-ping(a):
+		return a, nil
+	case <-ping(b):
+		return b, nil
+	case <-time.After(timeout):
+		return "", fmt.Errorf("timed out waiting for %s and %s", a, b)
+	}
+}
+func Racer(a, b string) (string, error) {
+	return ConfigurableRacer(a, b, tenSecondTimeout)
+}
+
+func measureResponseTime(url string) time.Duration {
+	start := time.Now()
+	http.Get(url)
+	return time.Since(start)
+}
+
+func ping(url string) chan struct{} {
+	ch := make(chan struct{})
+	go func() {
+		// close after http Get
+		http.Get(url)
+		close(ch)
+	}()
+	return ch
+}

select/select_test.go

@@ -0,0 +1,47 @@
+package select_sample
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+)
+
+func TestRacer(t *testing.T) {
+	t.Run("compares speeds of servers, returning the url of the fastest one", func(t *testing.T) {
+		slowServer := makeDelayServer(5 * time.Millisecond)
+		fastServer := makeDelayServer(0 * time.Millisecond)
+		defer slowServer.Close()
+		defer fastServer.Close()
+		slowURL := slowServer.URL
+		fastURL := fastServer.URL
+		want := fastURL
+		got, err := Racer(slowURL, fastURL)
+		if err != nil {
+			t.Errorf("error should be nit")
+		}
+		if got != want {
+			t.Errorf("got %q, want %q", got, want)
+		}
+	})
+	t.Run("returns an error if a server doesn't respond within the specified time", func(t *testing.T) {
+		server := makeDelayServer(25 * time.Millisecond)
+
+		defer server.Close()
+
+		_, err := ConfigurableRacer(server.URL, server.URL, 20*time.Millisecond)
+
+		if err == nil {
+			t.Error("expected an error but didn't get one")
+		}
+	})
+}
+
+func makeDelayServer(timeout time.Duration) *httptest.Server {
+	return httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			time.Sleep(timeout)
+			w.WriteHeader(http.StatusOK)
+		},
+	))
+}