Initial e2e test

Signed-off-by: Mohamed Hamza <mhamza15@github.com>

Author: mhamza15

go/test/endtoend/vtgate/sessionbalancer/main_test.go

@@ -0,0 +1,79 @@
+/*
+Copyright 2025 The Vitess Authors.
+
+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
+
+    http://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 sessionbalancer
+
+import (
+	_ "embed"
+	"flag"
+	"os"
+	"testing"
+
+	"vitess.io/vitess/go/mysql"
+	"vitess.io/vitess/go/test/endtoend/cluster"
+)
+
+var (
+	clusterInstance *cluster.LocalProcessCluster
+	vtParams        mysql.ConnParams
+	uks             = "uks"
+	cell            = "test_misc"
+
+	//go:embed uschema.sql
+	uschemaSQL string
+)
+
+func TestMain(m *testing.M) {
+	flag.Parse()
+
+	exitCode := func() int {
+		clusterInstance = cluster.NewCluster(cell, "localhost")
+		defer clusterInstance.Teardown()
+
+		// Start topo server
+		err := clusterInstance.StartTopo()
+		if err != nil {
+			return 1
+		}
+
+		// Enable session balancer in vtgate
+		clusterInstance.VtGateExtraArgs = append(clusterInstance.VtGateExtraArgs,
+			"--enable-balancer",
+			"--balancer-vtgate-cells", clusterInstance.Cell,
+			"--balancer-type", "session")
+
+		// Start keyspace with multiple tablets per shard
+		keyspace := &cluster.Keyspace{
+			Name:      uks,
+			SchemaSQL: uschemaSQL,
+		}
+		err = clusterInstance.StartUnshardedKeyspace(*keyspace, 2, false)
+		if err != nil {
+			return 1
+		}
+
+		// Start vtgate
+		err = clusterInstance.StartVtgate()
+		if err != nil {
+			return 1
+		}
+
+		vtParams = clusterInstance.GetVTParams(uks)
+
+		return m.Run()
+	}()
+	os.Exit(exitCode)
+}

go/test/endtoend/vtgate/sessionbalancer/session_test.go

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+/*
+Copyright 2025 The Vitess Authors.
+
+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
+
+    http://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 sessionbalancer
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"vitess.io/vitess/go/mysql"
+)
+
+// TestSessionBalancer validates that the session balancer consistently routes
+// queries for the same session to the same tablet.
+func TestSessionBalancer(t *testing.T) {
+	// Get connections that route to different tablets
+	conn1, conn2, id1, id2 := connections(t)
+
+	defer conn1.Close()
+	defer conn2.Close()
+
+	// Validate that each connection consistently returns the same server ID
+	for range 20 {
+		newID1 := serverID(t, conn1)
+		require.Equal(t, id1, newID1)
+
+		newID2 := serverID(t, conn2)
+		require.Equal(t, id2, newID2)
+
+		require.NotEqual(t, newID2, newID1)
+	}
+}
+
+// connections returns two connections that should route to different servers.
+func connections(t *testing.T) (conn1, conn2 *mysql.Conn, id1, id2 string) {
+	t.Helper()
+
+	// Keep creating connections until we find two that route to different server IDs
+	vtParams.DbName = uks + "@replica"
+	for {
+		conn1, err := mysql.Connect(context.Background(), &vtParams)
+		require.NoError(t, err)
+
+		conn2, err = mysql.Connect(context.Background(), &vtParams)
+		require.NoError(t, err)
+
+		id1 = serverID(t, conn1)
+		id2 = serverID(t, conn2)
+
+		// Break if we found connections with different server IDs
+		if id1 != id2 {
+			return conn1, conn2, id1, id2
+		}
+
+		// If not, close the connections and try again
+		conn1.Close()
+		conn2.Close()
+	}
+}
+
+// serverID runs a `SELECT @@server_id` on the given connection and returns the
+// server's ID.
+func serverID(t *testing.T, conn *mysql.Conn) string {
+	t.Helper()
+
+	result1, err := conn.ExecuteFetch("SELECT @@server_uuid", 1, false)
+	require.NoError(t, err)
+
+	tablet1Bytes, err := result1.Rows[0][0].ToBytes()
+	require.NoError(t, err)
+
+	return string(tablet1Bytes)
+}

go/test/endtoend/vtgate/sessionbalancer/uschema.sql

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+CREATE TABLE t1 (
+    id int PRIMARY KEY,
+    name varchar(255)
+);
+
+CREATE TABLE t2 (
+    id int PRIMARY KEY,
+    value varchar(255)
+);