Add TestFreePort(...) which just returns an available free localhost port (#964)

sdk/testutil/free_port.go

@@ -0,0 +1,21 @@
+package testutil
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestFreePort just returns an available free localhost port
+func TestFreePort(t *testing.T) int {
+	t.Helper()
+	require := require.New(t)
+	addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
+	require.NoError(err)
+
+	l, err := net.ListenTCP("tcp", addr)
+	require.NoError(err)
+	defer l.Close()
+	return l.Addr().(*net.TCPAddr).Port
+}

sdk/testutil/free_port_test.go

@@ -0,0 +1,25 @@
+package testutil
+
+import (
+	"fmt"
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_TestFreePort(t *testing.T) {
+	t.Parallel()
+	t.Run("simple-validation", func(t *testing.T) {
+		assert, require := assert.New(t), require.New(t)
+		p := TestFreePort(t)
+		assert.NotEmpty(p)
+
+		addr, err := net.ResolveTCPAddr("tcp", fmt.Sprintf("localhost:%d", p))
+		require.NoError(err)
+		l, err := net.ListenTCP("tcp", addr)
+		require.NoError(err)
+		defer l.Close()
+	})
+}