Fix TestOpen_openAndPingFails (#3551)

exp/services/recoverysigner/internal/db/db_test.go

@@ -1,6 +1,9 @@
 package db
 
 import (
+	"fmt"
+	"net"
+	"regexp"
 	"testing"
 
 	"github.com/stellar/go/support/db/dbtest"
@@ -20,10 +23,25 @@ func TestOpen_openAndPingSucceeds(t *testing.T) {
 }
 
 func TestOpen_openAndPingFails(t *testing.T) {
-	sqlxDB, err := Open("postgres://localhost:0")
+	// Find an empty port
+	listener, err := net.Listen("tcp", ":0")
+	require.NoError(t, err)
+	port := listener.Addr().(*net.TCPAddr).Port
+	require.NoError(t, listener.Close())
+	// Slight race here with other stuff on the system, which could claim this port.
+
+	sqlxDB, err := Open(fmt.Sprintf("postgres://localhost:%d", port))
 	require.NoError(t, err)
 	assert.Equal(t, "postgres", sqlxDB.DriverName())
 
 	err = sqlxDB.Ping()
-	require.EqualError(t, err, "dial tcp 127.0.0.1:0: connect: connection refused")
+	require.Error(t, err)
+	require.Regexp(
+		t,
+		regexp.MustCompile(
+			// regex to support both ipv4 and ipv6, on the port we found.
+			fmt.Sprintf("dial tcp (127\\.0\\.0\\.1|\\[::1\\]):%d: connect: connection refused", port),
+		),
+		err.Error(),
+	)
 }