credentials/alts: fix defer in TestDial (#7301)

credentials/alts/internal/handshaker/service/service.go

@@ -34,8 +34,6 @@ var (
 	// to a corresponding connection to a hypervisor handshaker service
 	// instance.
 	hsConnMap = make(map[string]*grpc.ClientConn)
-	// hsDialer will be reassigned in tests.
-	hsDialer = grpc.Dial
 )
 
 // Dial dials the handshake service in the hypervisor. If a connection has
@@ -50,7 +48,7 @@ func Dial(hsAddress string) (*grpc.ClientConn, error) {
 		// Create a new connection to the handshaker service. Note that
 		// this connection stays open until the application is closed.
 		var err error
-		hsConn, err = hsDialer(hsAddress, grpc.WithTransportCredentials(insecure.NewCredentials()))
+		hsConn, err = grpc.Dial(hsAddress, grpc.WithTransportCredentials(insecure.NewCredentials()))
 		if err != nil {
 			return nil, err
 		}

credentials/alts/internal/handshaker/service/service_test.go

@@ -21,34 +21,33 @@ package service
 import (
 	"testing"
 
-	grpc "google.golang.org/grpc"
+	"google.golang.org/grpc/internal/grpctest"
 )
 
+type s struct {
+	grpctest.Tester
+}
+
+func Test(t *testing.T) {
+	grpctest.RunSubTests(t, s{})
+}
+
 const (
 	testAddress1 = "some_address_1"
 	testAddress2 = "some_address_2"
 )
 
-func TestDial(t *testing.T) {
-	defer func() func() {
-		temp := hsDialer
-		hsDialer = func(target string, opts ...grpc.DialOption) (*grpc.ClientConn, error) {
-			return &grpc.ClientConn{}, nil
-		}
-		return func() {
-			hsDialer = temp
-		}
-	}()
-
+// TestDial verifies the behaviour of alts handshake when there are multiple Dials.
+// If a connection has already been established, this function returns it.
+// Otherwise, a new connection is created.
+func (s) TestDial(t *testing.T) {
 	// First call to Dial, it should create a connection to the server running
 	// at the given address.
 	conn1, err := Dial(testAddress1)
 	if err != nil {
 		t.Fatalf("first call to Dial(%v) failed: %v", testAddress1, err)
 	}
-	if conn1 == nil {
-		t.Fatalf("first call to Dial(%v)=(nil, _), want not nil", testAddress1)
-	}
+	defer conn1.Close()
 	if got, want := hsConnMap[testAddress1], conn1; got != want {
 		t.Fatalf("hsConnMap[%v]=%v, want %v", testAddress1, got, want)
 	}
@@ -58,22 +57,20 @@ func TestDial(t *testing.T) {
 	if err != nil {
 		t.Fatalf("second call to Dial(%v) failed: %v", testAddress1, err)
 	}
+	defer conn2.Close()
 	if got, want := conn2, conn1; got != want {
 		t.Fatalf("second call to Dial(%v)=(%v, _), want (%v,. _)", testAddress1, got, want)
 	}
 	if got, want := hsConnMap[testAddress1], conn1; got != want {
 		t.Fatalf("hsConnMap[%v]=%v, want %v", testAddress1, got, want)
 	}
 
-	// Third call to Dial using a different address should create a new
-	// connection.
+	// Third call to Dial using a different address should create a new connection.
 	conn3, err := Dial(testAddress2)
 	if err != nil {
 		t.Fatalf("third call to Dial(%v) failed: %v", testAddress2, err)
 	}
-	if conn3 == nil {
-		t.Fatalf("third call to Dial(%v)=(nil, _), want not nil", testAddress2)
-	}
+	defer conn3.Close()
 	if got, want := hsConnMap[testAddress2], conn3; got != want {
 		t.Fatalf("hsConnMap[%v]=%v, want %v", testAddress2, got, want)
 	}