amtool: fix panic if --verbose is in used.

Signed-off-by: Jan-Otto Kröpke <joe@cloudeteer.de>

cli/root.go

@@ -52,6 +52,7 @@ var (
 func initMatchersCompat(_ *kingpin.ParseContext) error {
 	promslogConfig := &promslog.Config{Writer: os.Stdout}
 	if verbose {
+		promslogConfig.Level = &promslog.AllowedLevel{}
 		_ = promslogConfig.Level.Set("debug")
 	}
 	logger := promslog.New(promslogConfig)
@@ -144,7 +145,7 @@ func NewAlertmanagerClient(amURL *url.URL) *client.AlertmanagerAPI {
 }
 
 // Execute is the main function for the amtool command.
-func Execute() {
+func Execute(args []string) {
 	app := kingpin.New("amtool", helpRoot).UsageWriter(os.Stdout)
 
 	format.InitFormatFlags(app)
@@ -175,12 +176,12 @@ func Execute() {
 
 	app.Action(initMatchersCompat)
 
-	err = resolver.Bind(app, os.Args[1:])
+	err = resolver.Bind(app, args[1:])
 	if err != nil {
 		kingpin.Fatalf("%v\n", err)
 	}
 
-	_, err = app.Parse(os.Args[1:])
+	_, err = app.Parse(args[1:])
 	if err != nil {
 		kingpin.Fatalf("%v\n", err)
 	}

cmd/amtool/main.go

@@ -13,8 +13,16 @@
 
 package main
 
-import "github.com/prometheus/alertmanager/cli"
+import (
+	"os"
+
+	"github.com/prometheus/alertmanager/cli"
+)
 
 func main() {
-	cli.Execute()
+	run(os.Args)
+}
+
+func run(args []string) {
+	cli.Execute(args)
 }

cmd/amtool/main_test.go

@@ -0,0 +1,103 @@
+// Copyright 2018 Prometheus Team
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"os/exec"
+	"runtime"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestEmptyCommand(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		args     []string
+		exitCode int
+		stdout   string
+		stderr   string
+	}{
+		{
+			name:     "help without command",
+			args:     []string{},
+			exitCode: 0,
+			stdout:   `usage: amtool [<flags>] <command> [<args> ...]`,
+		},
+		{
+			name:     "empty command",
+			args:     []string{""},
+			exitCode: 1,
+			stderr:   `error: expected command but got ""`,
+		},
+		{
+			name:   "version",
+			args:   []string{"--version"},
+			stdout: fmt.Sprintf("amtool, version  (branch: , revision: unknown)\n  build user:       \n  build date:       \n  go version:       %s\n  platform:         %s/%s\n  tags:             unknown\n", runtime.Version(), runtime.GOOS, runtime.GOARCH),
+		},
+		// In this test, we a running a command that invokes the --verbose flag.
+		// The test expects that there is no running instance on port 1.
+		{
+			name:     "verbose flag",
+			exitCode: 1,
+			args:     []string{"--verbose", "alert", "add", "--alertmanager.url=http://localhost:1"},
+			stderr:   `error: Post "http://localhost:1/api/v2/alerts": dial tcp 127.0.0.1:1`,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			if os.Getenv("FORK") == "1" {
+				run(append([]string{"amtool"}, tc.args...))
+			}
+
+			stdout, stderr, err := RunForkTest(t)
+
+			if tc.exitCode == 0 {
+				require.NoError(t, err, "STDOUT:\n%s\n\nSTDERR:\n%s", stdout, stderr)
+			} else {
+				require.EqualError(t, err, fmt.Sprintf("exit status %d", tc.exitCode), "STDOUT:\n%s\n\nSTDERR:\n%s", stdout, stderr)
+			}
+
+			if tc.stderr == "" {
+				require.Empty(t, stderr)
+			} else {
+				require.Contains(t, stderr, tc.stderr)
+			}
+
+			if tc.stdout == "" {
+				require.Empty(t, stdout)
+			} else {
+				require.Contains(t, stdout, tc.stdout)
+			}
+		})
+	}
+}
+
+func RunForkTest(t *testing.T) (string, string, error) {
+	t.Helper()
+
+	cmd := exec.Command(os.Args[0], fmt.Sprintf("-test.run=%v", t.Name()))
+	cmd.Env = append(os.Environ(), "FORK=1")
+
+	var stdoutB, stderrB bytes.Buffer
+	cmd.Stdin = nil
+	cmd.Stdout = &stdoutB
+	cmd.Stderr = &stderrB
+
+	err := cmd.Run()
+
+	return stdoutB.String(), stderrB.String(), err
+}