Add ConfigFlag for loading configuration through a flag.

util_test.go

@@ -0,0 +1,44 @@
+package kong
+
+import (
+	"io/ioutil"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestConfigFlag(t *testing.T) {
+	var cli struct {
+		Config ConfigFlag
+		Flag   string
+	}
+
+	w, err := ioutil.TempFile("", "")
+	require.NoError(t, err)
+	defer os.Remove(w.Name())
+	w.WriteString(`{"flag": "hello world"}`) // nolint: errcheck
+	w.Close()
+
+	p := Must(&cli, Configuration(JSON))
+	_, err = p.Parse([]string{"--config", w.Name()})
+	require.NoError(t, err)
+	require.Equal(t, "hello world", cli.Flag)
+}
+
+func TestVersionFlag(t *testing.T) {
+	var cli struct {
+		Version VersionFlag
+	}
+	w := &strings.Builder{}
+	p := Must(&cli, Vars{"version": "0.1.1"})
+	p.Stdout = w
+	called := 1
+	p.Exit = func(s int) { called = s }
+
+	_, err := p.Parse([]string{"--version"})
+	require.NoError(t, err)
+	require.Equal(t, "0.1.1", strings.TrimSpace(w.String()))
+	require.Equal(t, 0, called)
+}