# Building a Test Application

Often, you will want to test your newly written plugin in an as small setting as possible. Ususally, `gst-launch` is a good first step at testing a plugin. However, you will often need more testing features than gst-launch can provide, such as seeking, events, interactivity and more. Writing your own small testing program is the easiest way to accomplish this. This section explains - in a few words - how to do that. For a complete application development guide, see the Application Development Manual.

At the start, you need to initialize the &GStreamer; core library by calling `gst_init ()`. You can alternatively call `gst_init_with_popt_tables ()`, which will return a pointer to popt tables. You can then use libpopt to handle the given argument table, and this will finish the &GStreamer; intialization.

You can create elements using `gst_element_factory_make ()`, where the first argument is the element type that you want to create, and the second argument is a free-form name. The example at the end uses a simple filesource - decoder - soundcard output pipeline, but you can use specific debugging elements if that's necessary. For example, an `identity` element can be used in the middle of the pipeline to act as a data-to-application transmitter. This can be used to check the data for misbehaviours or correctness in your test application. Also, you can use a `fakesink` element at the end of the pipeline to dump your data to the stdout (in order to do this, set the `dump` property to TRUE). Lastly, you can use the `efence` element (indeed, an eletric fence memory debugger wrapper element) to check for memory errors.

During linking, your test application can use fixation or filtered caps as a way to drive a specific type of data to or from your element. This is a very simple and effective way of checking multiple types of input and output in your element.

Running the pipeline happens through the `gst_bin_iterate ()` function. Note that during running, you should connect to at least the error and eos signals on the pipeline and/or your plugin/element to check for correct handling of this. Also, you should add events into the pipeline and make sure your plugin handles these correctly (with respect to clocking, internal caching, etc.).

Never forget to clean up memory in your plugin or your test application. When going to the NULL state, your element should clean up allocated memory and caches. Also, it should close down any references held to possible support libraries. Your application should `unref ()` the pipeline and make sure it doesn't crash.

    #include <gst/gst.h>

    gint
    main (gint   arcg,
          gchar *argv[])
    {
      GstElement *pipeline, *filesrc, *decoder, *filter, *sink;

      /* initialization */
      gst_init (&argc, &argv);

      /* create elements */
      pipeline = gst_pipeline_new ("my_pipeline");

      filesrc  = gst_element_factory_make ("filesrc", "my_filesource");
      decoder  = gst_element_factory_make ("mad", "my_decoder");
      filter   = gst_element_factory_make ("my_filter", "my_filter");
      sink     = gst_element_factory_make ("osssink", "audiosink");

      g_object_set (G_OBJECT (filesrc), "location", argv[1], NULL);

      /* link everything together */
      gst_element_link_many (filesrc, decoder, filter, sink, NULL);
      gst_bin_add_many (GST_BIN (pipeline), filesrc, decoder, filter, sink, NULL);

      /* run */
      gst_element_set_state (pipeline, GST_STATE_PLAYING);
      while (gst_bin_iterate (GST_BIN (pipeline)));

      /* clean up */
      gst_element_set_state (pipeline, GST_STATE_NULL);
      gst_object_unref (GST_OBJECT (pipeline));

      return 0;
    }