test: added program "read_mixer"

This little program is used to test mixer plugins in an isolated
environment.  This is ALSA-only currently, because we don't have a
real "plugin list" yet, and I'm too lazy to implement a switch.

test/read_mixer.c

@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "mixer_control.h"
+#include "mixer_list.h"
+
+#include <glib.h>
+
+#include <assert.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(int argc, G_GNUC_UNUSED char **argv)
+{
+	struct mixer *mixer;
+	bool success;
+	int volume;
+
+	if (argc != 2) {
+		g_printerr("Usage: read_mixer PLUGIN\n");
+		return 1;
+	}
+
+	g_thread_init(NULL);
+
+	mixer = mixer_new(&alsa_mixer, NULL);
+	if (mixer == NULL) {
+		g_printerr("mixer_new() failed\n");
+		return 2;
+	}
+
+	success = mixer_open(mixer);
+	if (!success) {
+		mixer_free(mixer);
+		g_printerr("failed to open the mixer\n");
+		return 2;
+	}
+
+	volume = mixer_get_volume(mixer);
+	mixer_close(mixer);
+	mixer_free(mixer);
+
+	assert(volume >= -1 && volume <= 100);
+
+	if (volume < 0) {
+		g_printerr("failed to read volume\n");
+		return 2;
+	}
+
+	g_print("%d\n", volume);
+	return 0;
+}