A few extra fixes and tests.

config_test.go

@@ -0,0 +1,54 @@
+package kong_test
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/alecthomas/kong"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMultipleConfigLoading(t *testing.T) {
+	var cli struct {
+		Flag string `json:"flag,omitempty"`
+	}
+
+	cli.Flag = "first"
+	first, cleanFirst := makeConfig(t, &cli)
+	defer cleanFirst()
+
+	cli.Flag = ""
+	second, cleanSecond := makeConfig(t, &cli)
+	defer cleanSecond()
+
+	p := mustNew(t, &cli, kong.Configuration(kong.JSON, first, second))
+	_, err := p.Parse(nil)
+	require.NoError(t, err)
+	require.Equal(t, "first", cli.Flag)
+}
+
+func TestConfigValidation(t *testing.T) {
+	var cli struct {
+		Flag string `json:"flag,omitempty" enum:"valid"`
+	}
+
+	cli.Flag = "invalid"
+	conf, cleanConf := makeConfig(t, &cli)
+	defer cleanConf()
+
+	p := mustNew(t, &cli, kong.Configuration(kong.JSON, conf))
+	_, err := p.Parse(nil)
+	require.Error(t, err)
+}
+
+func makeConfig(t *testing.T, config interface{}) (path string, cleanup func()) {
+	t.Helper()
+	w, err := ioutil.TempFile("", "")
+	require.NoError(t, err)
+	defer w.Close()
+	err = json.NewEncoder(w).Encode(config)
+	require.NoError(t, err)
+	return w.Name(), func() { os.Remove(w.Name()) }
+}