cmd/ethkey: fix formatting, review nits (#15807)

This commit:

- Adds a --msgfile option to read the message to sign from a file
  instead of command line argument.
- Adds a unit test for signing subcommands.
- Removes some weird whitespace in the code.

cmd/ethkey/run_test.go

@@ -0,0 +1,54 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/docker/docker/pkg/reexec"
+	"github.com/ethereum/go-ethereum/internal/cmdtest"
+)
+
+type testEthkey struct {
+	*cmdtest.TestCmd
+}
+
+// spawns ethkey with the given command line args.
+func runEthkey(t *testing.T, args ...string) *testEthkey {
+	tt := new(testEthkey)
+	tt.TestCmd = cmdtest.NewTestCmd(t, tt)
+	tt.Run("ethkey-test", args...)
+	return tt
+}
+
+func TestMain(m *testing.M) {
+	// Run the app if we've been exec'd as "ethkey-test" in runEthkey.
+	reexec.Register("ethkey-test", func() {
+		if err := app.Run(os.Args); err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		os.Exit(0)
+	})
+	// check if we have been reexec'd
+	if reexec.Init() {
+		return
+	}
+	os.Exit(m.Run())
+}