Add test for WithVersion option (#8)

protoplugin.go

@@ -131,9 +131,9 @@ func run(
 			_, err := fmt.Fprintln(stdout, runOptions.version)
 			return err
 		}
-		return fmt.Errorf("unknown argument: %s", args[0])
+		return newUnknownArgumentsError(args)
 	default:
-		return fmt.Errorf("unknown arguments: %v", strings.Join(args, " "))
+		return newUnknownArgumentsError(args)
 	}
 
 	if runOptions.warningHandlerFunc == nil {
@@ -210,3 +210,18 @@ func (f mainOptionsFunc) applyMainOption(runOptions *runOptions) {
 func (f mainOptionsFunc) applyRunOption(runOptions *runOptions) {
 	f(runOptions)
 }
+
+type unknownArgumentsError struct {
+	args []string
+}
+
+func newUnknownArgumentsError(args []string) error {
+	return &unknownArgumentsError{args: args}
+}
+
+func (e *unknownArgumentsError) Error() string {
+	if len(e.args) == 1 {
+		return fmt.Sprintf("unknown argument: %s", e.args[0])
+	}
+	return fmt.Sprintf("unknown arguments: %s", strings.Join(e.args, " "))
+}

protoplugin_test.go

@@ -22,6 +22,7 @@ import (
 	"sort"
 	"strings"
 	"testing"
+	"testing/iotest"
 
 	"github.com/bufbuild/protocompile"
 	"github.com/bufbuild/protocompile/protoutil"
@@ -68,6 +69,38 @@ func TestBasic(t *testing.T) {
 	)
 }
 
+func TestWithVersionOption(t *testing.T) {
+	t.Parallel()
+
+	run := func(args []string, runOptions ...RunOption) (string, error) {
+		stdout := bytes.NewBuffer(nil)
+		err := Run(
+			context.Background(),
+			args,
+			iotest.ErrReader(io.EOF),
+			stdout,
+			io.Discard,
+			HandlerFunc(func(ctx context.Context, w *ResponseWriter, r *Request) error { return nil }),
+			runOptions...,
+		)
+		return stdout.String(), err
+	}
+
+	var unknownArgumentsError *unknownArgumentsError
+	_, err := run([]string{"--unsupported"})
+	require.ErrorAs(t, err, &unknownArgumentsError)
+	_, err = run([]string{"--unsupported"}, WithVersion("0.0.1"))
+	require.ErrorAs(t, err, &unknownArgumentsError)
+	_, err = run([]string{"--version"})
+	require.ErrorAs(t, err, &unknownArgumentsError)
+	_, err = run([]string{"--foo", "--bar"})
+	require.ErrorAs(t, err, &unknownArgumentsError)
+
+	out, err := run([]string{"--version"}, WithVersion("0.0.1"))
+	require.NoError(t, err)
+	require.Equal(t, "0.0.1\n", out)
+}
+
 func testBasic(
 	t *testing.T,
 	fileToGenerate []string,