Test that a shared miss keeps its deadline and reports panics (closes #65)

A request with a deadline whose fetch waits on its context, as the
fetcher does while it waits for a free connection to the host, must
return by that deadline. A panic while a variant is being made must be
reported through the Sentry hub on the request's context, where the
Sentry middleware puts one when sentry_dsn is set. The panic test fails
on next, where the panic leaves Get.

Model: opus-5-5

internal/imgcache/concurrent_misses_internal_test.go

@@ -13,6 +13,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/getsentry/sentry-go"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/magic"
 )
@@ -408,6 +409,32 @@ func TestService_Get_EndedRequestFetchesNothing(t *testing.T) {
 	}
 }
 
+// TestService_Get_ReturnsByItsDeadline gives a request a deadline and holds
+// its fetch until the fetch's context ends, as the fetcher does while it waits
+// for a free connection to the host. The request must return by its deadline
+// with the deadline's error.
+func TestService_Get_ReturnsByItsDeadline(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures, _ := setupHeldFetchService(t)
+
+	const timeout = 200 * time.Millisecond
+
+	ctx, cancel := context.WithTimeout(t.Context(), timeout)
+	defer cancel()
+
+	results := startGet(ctx, svc, photoVariant(fixtures, 85, FitCover))
+
+	select {
+	case got := <-results:
+		if !errors.Is(got.err, context.DeadlineExceeded) {
+			t.Errorf("Get() error = %v, want %v", got.err, context.DeadlineExceeded)
+		}
+	case <-time.After(timeout + time.Second):
+		t.Fatal("request did not return by its deadline")
+	}
+}
+
 // panickingFetcher panics on every fetch.
 type panickingFetcher struct{}
 
@@ -442,3 +469,41 @@ func TestService_Get_PanicBecomesAnError(t *testing.T) {
 		t.Errorf("Get() error = %v, want one naming the panic", err)
 	}
 }
+
+// TestService_Get_PanicIsReportedToSentry checks that a panic while a variant
+// is being made is reported through the Sentry hub on the request's context,
+// where the Sentry middleware puts one when sentry_dsn is set.
+func TestService_Get_PanicIsReportedToSentry(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures := SetupTestService(t)
+	svc.fetcher = panickingFetcher{}
+
+	transport := &sentry.MockTransport{}
+
+	client, err := sentry.NewClient(sentry.ClientOptions{
+		Dsn:       "https://abc123@sentry.example.com/42",
+		Transport: transport,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx := sentry.SetHubOnContext(t.Context(),
+		sentry.NewHub(client, sentry.NewScope()))
+
+	func() {
+		defer func() {
+			if recovered := recover(); recovered != nil {
+				t.Fatalf("Get() panicked: %v", recovered)
+			}
+		}()
+
+		_, _ = svc.Get(ctx, photoVariant(fixtures, 85, FitCover))
+	}()
+
+	events := transport.Events()
+	if len(events) != 1 || events[0].Message != "upstream fetcher panicked" {
+		t.Errorf("Sentry events = %+v, want one for the panic", events)
+	}
+}