Set chunkSize when creating a new GCS backend (#6655)

Adds a small step to TestBackend to prevent regression.

physical/gcs/gcs.go

@@ -158,9 +158,9 @@ func NewBackend(c map[string]string, logger log.Logger) (physical.Backend, error
 	}
 
 	return &Backend{
-		bucket:    bucket,
-		haEnabled: haEnabled,
-
+		bucket:     bucket,
+		haEnabled:  haEnabled,
+		chunkSize:  chunkSize,
 		client:     client,
 		permitPool: physical.NewPermitPool(maxParallel),
 		logger:     logger,

physical/gcs/gcs_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"math/rand"
 	"os"
+	"strconv"
 	"testing"
 	"time"
 
@@ -57,6 +58,17 @@ func TestBackend(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// Verify chunkSize is set correctly on the Backend
+	be := backend.(*Backend)
+	expectedChunkSize, err := strconv.Atoi(defaultChunkSize)
+	if err != nil {
+		t.Fatalf("failed to convert defaultChunkSize to int: %s", err)
+	}
+	expectedChunkSize = expectedChunkSize * 1024
+	if be.chunkSize != expectedChunkSize {
+		t.Fatalf("expected chunkSize to be %d. got=%d", expectedChunkSize, be.chunkSize)
+	}
+
 	physical.ExerciseBackend(t, backend)
 	physical.ExerciseBackend_ListPrefix(t, backend)
 }