test: pin the production receive limits, split the vacuous drain test, harden the lint-gate test (review of #55)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

cmd/tapir/shutdown_test.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"sync"
 	"syscall"
 	"testing"
 	"time"
@@ -32,9 +33,20 @@ func TestShutdownContext_IsCancelledBySIGTERMAndSIGINT(t *testing.T) {
 }
 
 // serveHTTP must not return while a request is in flight or the worker is still recording
-// its job: ListenAndServe returns ErrServerClosed the moment Shutdown starts, so returning
-// from it let the process exit before either finished (#50).
-func TestServeHTTP_ReturnsOnlyAfterTheInFlightRequestAndTheWorkerHaveFinished(t *testing.T) {
+// its job: Serve returns http.ErrServerClosed as soon as Shutdown STARTS, and returning
+// from it let the process exit before either finished (#50). Each half is tested with the
+// other already satisfied, so neither can hold the call open on the other's behalf.
+
+func pendingFor(t *testing.T, returned <-chan error, why string) {
+	t.Helper()
+	select {
+	case err := <-returned:
+		t.Fatalf("serveHTTP returned (%v) %s", err, why)
+	case <-time.After(150 * time.Millisecond):
+	}
+}
+
+func TestServeHTTP_DrainsAnInFlightRequestBeforeReturning(t *testing.T) {
 	release := make(chan struct{})
 	entered := make(chan struct{})
 	srv := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
@@ -44,8 +56,12 @@ func TestServeHTTP_ReturnsOnlyAfterTheInFlightRequestAndTheWorkerHaveFinished(t
 	}))
 	srv.Start()
 	defer srv.Close()
+	var once sync.Once
+	releaseHandler := func() { once.Do(func() { close(release) }) }
+	defer releaseHandler() // runs before srv.Close: a failing test must not hang on the blocked handler
 	ctx, cancel := context.WithCancel(context.Background())
 	workerDone := make(chan struct{})
+	close(workerDone) // the worker is already done: only the request can hold serveHTTP open
 	returned := make(chan error, 1)
 	go func() { returned <- serveHTTP(ctx, srv.Config, srv.Listener, nil, workerDone, 5*time.Second) }()
 
@@ -53,17 +69,30 @@ func TestServeHTTP_ReturnsOnlyAfterTheInFlightRequestAndTheWorkerHaveFinished(t
 	<-entered
 	cancel()
 
-	assertPending := func(why string) {
-		t.Helper()
-		select {
-		case err := <-returned:
-			t.Fatalf("serveHTTP returned (%v) %s", err, why)
-		case <-time.After(150 * time.Millisecond):
+	pendingFor(t, returned, "while a request was still in flight")
+	releaseHandler()
+	select {
+	case err := <-returned:
+		if err != nil {
+			t.Fatalf("serveHTTP: %v", err)
 		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("serveHTTP did not return once the request finished")
 	}
-	assertPending("while a request was still in flight")
-	close(release)
-	assertPending("before the worker finished")
+}
+
+func TestServeHTTP_WaitsForTheWorkerBeforeReturning(t *testing.T) {
+	srv := httptest.NewUnstartedServer(http.NotFoundHandler())
+	srv.Start()
+	defer srv.Close()
+	ctx, cancel := context.WithCancel(context.Background())
+	workerDone := make(chan struct{})
+	returned := make(chan error, 1)
+	go func() { returned <- serveHTTP(ctx, srv.Config, srv.Listener, nil, workerDone, 5*time.Second) }() // no request in flight
+
+	cancel()
+
+	pendingFor(t, returned, "before the worker finished")
 	close(workerDone)
 	select {
 	case err := <-returned:
@@ -71,7 +100,7 @@ func TestServeHTTP_ReturnsOnlyAfterTheInFlightRequestAndTheWorkerHaveFinished(t
 			t.Fatalf("serveHTTP: %v", err)
 		}
 	case <-time.After(2 * time.Second):
-		t.Fatal("serveHTTP did not return once the request and the worker had finished")
+		t.Fatal("serveHTTP did not return once the worker finished")
 	}
 }