internal/gomote: fix flaky TestWriteFileFromURL test

This change fixes a flaky test introduced in CL 397596.
The test was unnecessarily downloading a file from the go.dev site.
It was also not providing enough data to fix the issue when the test
failed.

Fixes golang/go#52671

Change-Id: Ie42501c197395538376debd510cfb993d697401d
Reviewed-on: https://go-review.googlesource.com/c/build/+/405516
Run-TryBot: Carlos Amedee <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
Auto-Submit: Carlos Amedee <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>

Author: cagedmantis

internal/gomote/gomote.go

@@ -478,7 +478,7 @@ func (s *Server) WriteFileFromURL(ctx context.Context, req *protos.WriteFileFrom
 			return nil, status.Errorf(codes.Aborted, "failed to get file from URL: %s", err)
 		}
 		if resp.StatusCode != http.StatusOK {
-			return nil, status.Errorf(codes.Aborted, "unable to get file from URL: response code: %d", resp.StatusCode)
+			return nil, status.Errorf(codes.Aborted, "unable to get file from %q: response code: %d", req.GetUrl(), resp.StatusCode)
 		}
 		rc = resp.Body
 	}

internal/gomote/gomote_test.go

@@ -12,6 +12,8 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 	"time"
 
@@ -788,9 +790,13 @@ func TestWriteFileFromURL(t *testing.T) {
 	ctx := access.FakeContextWithOutgoingIAPAuth(context.Background(), fakeIAP())
 	client := setupGomoteTest(t, context.Background())
 	gomoteID := mustCreateInstance(t, client, fakeIAP())
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintln(w, "Go is an open source programming language")
+	}))
+	defer ts.Close()
 	if _, err := client.WriteFileFromURL(ctx, &protos.WriteFileFromURLRequest{
 		GomoteId: gomoteID,
-		Url:      `https://go.dev/dl/go1.17.6.linux-amd64.tar.gz`,
+		Url:      ts.URL,
 		Filename: "foo",
 		Mode:     0777,
 	}); err != nil {