test: method fetch

main.go

@@ -30,30 +30,39 @@ func (l LastValues) String() string {
 	return fmt.Sprintf("Confirmed: %d, Deaths: %d, Recovered: %d", l.Confirmed, l.Deaths, l.Recovered)
 }
 
+// fetch runs on its own goroutine
+func fetch(ctx context.Context, req *http.Request, ch chan LastValues) error {
+	defer close(ch)
+	var r struct {
+		Data LastValues `json:"data"`
+	}
+	body, err := http.DefaultClient.Do(req)
+	if err != nil {
+		log.Printf("fetchCOVID19Data: %v", err)
+		return err
+	}
+	defer body.Body.Close()
+	err = json.NewDecoder(body.Body).Decode(&r)
+	if err != nil {
+		log.Printf("fetchCOVID19Data: %v", err)
+		return err
+	}
+
+	select {
+	case ch <- LastValues{r.Data.Confirmed, r.Data.Deaths, r.Data.Recovered}:
+	case <-ctx.Done():
+	}
+	return nil
+}
+
 // fetchCOVID19Data ...
-func fetchCOVID19Data(ctx context.Context, req *http.Request) <-chan LastValues {
+func fetchCOVID19Data(ctx context.Context) <-chan LastValues {
 	ch := make(chan LastValues)
-	go func() {
-		var r struct {
-			Data LastValues `json:"data"`
-		}
-		body, err := http.DefaultClient.Do(req)
-		if err != nil {
-			log.Printf("fetchCOVID19Data: %v", err)
-			return
-		}
-		defer body.Body.Close()
-		err = json.NewDecoder(body.Body).Decode(&r)
-		if err != nil {
-			log.Printf("fetchCOVID19Data: %v", err)
-			return
-		}
-
-		select {
-		case ch <- LastValues{r.Data.Confirmed, r.Data.Deaths, r.Data.Recovered}:
-		case <-ctx.Done():
-		}
-	}()
+	req, err := http.NewRequestWithContext(ctx, "GET", URL, nil)
+	if err != nil {
+		panic("internal error - misuse of NewRequestWithContext")
+	}
+	go fetch(ctx, req, ch)
 	return ch
 }
 
@@ -62,12 +71,8 @@ func routine(sleep time.Duration) {
 	const timeout = time.Second * 2
 	for {
 		ctx, cancel := context.WithTimeout(context.Background(), timeout)
-		req, err := http.NewRequestWithContext(ctx, "GET", URL, nil)
-		if err != nil {
-			panic("internal error - misuse of NewRequestWithContext")
-		}
 		select {
-		case newVal := <-fetchCOVID19Data(ctx, req):
+		case newVal := <-fetchCOVID19Data(ctx):
 			if cachedVal != newVal {
 				err := beeep.Alert("COVID-19 Brazil", newVal.String(), IMG)
 				if err != nil {

main_test.go

@@ -1,6 +1,11 @@
 package main
 
 import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
 	"testing"
 )
 
@@ -30,3 +35,35 @@ func TestLastValues_String(t *testing.T) {
 		})
 	}
 }
+
+func TestFetch(t *testing.T) {
+	tests := []struct {
+		name  string
+		input io.Reader
+		want  bool
+	}{
+		{"ok json", strings.NewReader(`{"data": {"confirmed": 10, "deaths": 10, "recovered": 10}}`), true},
+		{"bad json", strings.NewReader(`{"data": "confirmed": 10, "deaths": 10, "recovered": 10}}`), false},
+	}
+	for _, v := range tests {
+		v := v
+		t.Run(v.name, func(t *testing.T) {
+			t.Parallel()
+			ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				io.Copy(w, v.input)
+			}))
+			defer ts.Close()
+			req, err := http.NewRequest("GET", ts.URL, nil)
+			if err != nil {
+				panic("misuse of NewRequest")
+			}
+			ch := make(chan LastValues)
+			go func() { // drain the fetch output out
+				_ = <-ch
+			}()
+			if err := fetch(context.TODO(), req, ch); (err == nil) != v.want {
+				t.Errorf("fetch: expected: %v got: %v", v.want, err)
+			}
+		})
+	}
+}