test(spanner): Add integration test to check that requests with large message sizes that are under the limit succeed (#5392)

* Add integration test to check that requests with large message sizes that are under the limit succeed

* Remove debugging log

* Apply gemini suggested code review
* Remove redunant ctx initialization
* Fix comment typo
* Replace "math/rand" with "crypto/rand"

* formatting fixes

---------

Co-authored-by: rahul2393 <[email protected]>

Author: kinsaurralde

spanner/spanner_snippets/spanner/integration_test.go

@@ -1332,6 +1332,17 @@ func TestAddSplitPointsSample(t *testing.T) {
 	assertContains(t, out, "Added split points")
 }
 
+func TestTxWithLargeMessageSize(t *testing.T) {
+	_ = testutil.SystemTest(t)
+	t.Parallel()
+
+	_, dbName, cleanup := initTest(t, randomID())
+	defer cleanup()
+
+	mustRunSample(t, createDatabase, dbName, "failed to create a database")
+	runSample(t, writeLargeData, dbName, "failed to write large data")
+}
+
 func maybeCreateKey(projectId, locationId, keyRingId, keyId string) error {
 	client, err := kms.NewKeyManagementClient(context.Background())
 	if err != nil {

spanner/spanner_snippets/spanner/spanner_insert_large_data.go

@@ -0,0 +1,56 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package spanner
+
+// [START spanner_insert_large_data]
+
+import (
+	"context"
+	"crypto/rand"
+	"io"
+	"time"
+
+	"cloud.google.com/go/spanner"
+)
+
+func writeLargeData(w io.Writer, db string) error {
+	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
+	defer cancel()
+	client, err := spanner.NewClient(ctx, db)
+	if err != nil {
+		return err
+	}
+	defer client.Close()
+
+	singerColumns := []string{"SingerId", "FirstName", "LastName", "SingerInfo"}
+	token := make([]byte, 10000000)
+	if _, err := rand.Read(token); err != nil {
+		return err
+	}
+	// Mutation is under the 100MB limit
+	m := []*spanner.Mutation{
+		spanner.InsertOrUpdate("Singers", singerColumns, []interface{}{1, "Marc", "Richards", token}),
+		spanner.InsertOrUpdate("Singers", singerColumns, []interface{}{2, "Catalina", "Smith", token}),
+		spanner.InsertOrUpdate("Singers", singerColumns, []interface{}{3, "Alice", "Trentor", token}),
+		spanner.InsertOrUpdate("Singers", singerColumns, []interface{}{4, "Lea", "Martin", token}),
+		spanner.InsertOrUpdate("Singers", singerColumns, []interface{}{5, "David", "Lomond", token}),
+		spanner.InsertOrUpdate("Singers", singerColumns, []interface{}{6, "Marc", "Richards", token}),
+		spanner.InsertOrUpdate("Singers", singerColumns, []interface{}{7, "Catalina", "Smith", token}),
+	}
+	_, err = client.Apply(ctx, m)
+	return err
+}
+
+// [END spanner_insert_large_data]