sql/schemachanger: extend TestServer factory for shared servers

Previously, we only supported running a closure against a TestServer in
the schema changer testing framework. This was problematic for tests
that could save time by sharing servers (for example BACKUP / RESTORE).
To address this, this patch introduces a Start method for starting up a
server.

Release note: None

Author: fqazi

pkg/ccl/schemachangerccl/multiregion_testcluster_factory.go

@@ -56,10 +56,8 @@ func (f MultiRegionTestClusterFactory) WithSchemaLockDisabled() sctest.TestServe
 	return f
 }
 
-// Run implements the sctest.TestServerFactory interface.
-func (f MultiRegionTestClusterFactory) Run(
-	ctx context.Context, t *testing.T, fn func(_ serverutils.TestServerInterface, _ *gosql.DB),
-) {
+// Start implements the sctest.TestServerFactory interface.
+func (f MultiRegionTestClusterFactory) Start(ctx context.Context, t *testing.T) sctest.TestServer {
 	const numServers = 3
 	knobs := base.TestingKnobs{
 		SQLEvalContext: &eval.TestingKnobs{
@@ -83,6 +81,19 @@ func (f MultiRegionTestClusterFactory) Run(
 	}
 	sql.CreateTableWithSchemaLocked.Override(ctx, &st.SV, !f.schemaLockedDisabled)
 	c, db, _ := multiregionccltestutils.TestingCreateMultiRegionCluster(t, numServers, knobs, multiregionccltestutils.WithSettings(st))
-	defer c.Stopper().Stop(ctx)
-	fn(c.Server(0), db)
+	return sctest.TestServer{
+		Server: c.Server(0),
+		DB:     db,
+		Stopper: func(t *testing.T) {
+			c.Stopper().Stop(ctx)
+		},
+	}
+}
+
+func (f MultiRegionTestClusterFactory) Run(
+	ctx context.Context, t *testing.T, fn func(s serverutils.TestServerInterface, tdb *gosql.DB),
+) {
+	s := f.Start(ctx, t)
+	defer s.Stopper(t)
+	fn(s.Server, s.DB)
 }

pkg/sql/schemachanger/sctest/test_server_factory.go

@@ -25,6 +25,13 @@ import (
 	"github.com/cockroachdb/errors"
 )
 
+// TestServer is a test cluster and associated test database.
+type TestServer struct {
+	Server  serverutils.TestServerInterface
+	DB      *gosql.DB
+	Stopper func(t *testing.T)
+}
+
 // TestServerFactory constructs test clusters for declarative schema changer
 // end-to-end tests.
 type TestServerFactory interface {
@@ -48,6 +55,12 @@ type TestServerFactory interface {
 		t *testing.T,
 		fn func(s serverutils.TestServerInterface, tdb *gosql.DB),
 	)
+
+	// Start creates a test cluster and returns a TestServer.
+	Start(
+		ctx context.Context,
+		t *testing.T,
+	) TestServer
 }
 
 // SingleNodeTestClusterFactory is the vanilla implementation of
@@ -85,8 +98,15 @@ func (f SingleNodeTestClusterFactory) WithSchemaLockDisabled() TestServerFactory
 
 // Run implements the TestServerFactory interface.
 func (f SingleNodeTestClusterFactory) Run(
-	ctx context.Context, t *testing.T, fn func(_ serverutils.TestServerInterface, _ *gosql.DB),
+	ctx context.Context, t *testing.T, fn func(s serverutils.TestServerInterface, tdb *gosql.DB),
 ) {
+	s := f.Start(ctx, t)
+	defer s.Stopper(t)
+	fn(s.Server, s.DB)
+}
+
+// Start implements the TestServerFactory interface.
+func (f SingleNodeTestClusterFactory) Start(ctx context.Context, t *testing.T) TestServer {
 	args := base.TestServerArgs{
 		Knobs: base.TestingKnobs{
 			SQLEvalContext: &eval.TestingKnobs{
@@ -113,10 +133,14 @@ func (f SingleNodeTestClusterFactory) Run(
 	}
 	sql.CreateTableWithSchemaLocked.Override(ctx, &args.Settings.SV, !f.schemaLockedDisabled)
 	s, db, _ := serverutils.StartServer(t, args)
-	defer func() {
-		s.Stopper().Stop(ctx)
-	}()
-	fn(s, db)
+
+	return TestServer{
+		Server: s,
+		DB:     db,
+		Stopper: func(t *testing.T) {
+			s.Stopper().Stop(ctx)
+		},
+	}
 }
 
 // OldVersionKey is the version key used by the WithMixedVersion method