libbeat/cmd/instance: ensure test config file has appropriate permiss…

…ions (elastic#27178)

Git does not store r/w permissions, instead depending on the host system's
umask. On some systems the default umask is 0o002, meaning that the test
config file is checked out with g+w permission, causing the test to fail.

This change ensures that the test config is owner-exclusive write before
running the test. It also adds checks to currently ineffective error
assignments.

libbeat/cmd/instance/beat_test.go

@@ -78,16 +78,31 @@ func TestInitKibanaConfig(t *testing.T) {
 	assert.Equal(t, "testidx", b.Info.IndexPrefix)
 	assert.Equal(t, "0.9", b.Info.Version)
 
-	cfg, err := cfgfile.Load("../test/filebeat_test.yml", nil)
+	const configPath = "../test/filebeat_test.yml"
+
+	// Ensure that the config has owner-exclusive write permissions.
+	// This is necessary on some systems which have a default umask
+	// of 0o002, meaning that files are checked out by git with mode
+	// 0o664. This would cause cfgfile.Load to fail.
+	err = os.Chmod(configPath, 0o644)
+	assert.NoError(t, err)
+
+	cfg, err := cfgfile.Load(configPath, nil)
+	assert.NoError(t, err)
 	err = cfg.Unpack(&b.Config)
 	assert.NoError(t, err)
 
 	kibanaConfig := InitKibanaConfig(b.Config)
 	username, err := kibanaConfig.String("username", -1)
+	assert.NoError(t, err)
 	password, err := kibanaConfig.String("password", -1)
+	assert.NoError(t, err)
 	api_key, err := kibanaConfig.String("api_key", -1)
+	assert.NoError(t, err)
 	protocol, err := kibanaConfig.String("protocol", -1)
+	assert.NoError(t, err)
 	host, err := kibanaConfig.String("host", -1)
+	assert.NoError(t, err)
 
 	assert.Equal(t, "elastic-test-username", username)
 	assert.Equal(t, "elastic-test-password", password)