Harness

Object Hierarchy:

Gst.Check.Harness Gst.Check.Harness Gst.Check.Harness

Description:

[ CCode ( cname = "GstHarness" , has_type_id = false ) ]
[ GIR ( name = "Harness" ) ]
[ Version ( since = "1.6" ) ]
public struct Harness

Harness is meant to make writing unit test for GStreamer much easier.

It can be thought of as a way of treating a Element as a black box, deterministically feeding it data, and controlling what data it outputs.

The basic structure of Harness is two "floating" Pads that connect to the harnessed Element src and sink Pads like so:

          __________________________
 _____   |  _____            _____  |   _____
|     |  | |     |          |     | |  |     |
| src |--+-| sink|  Element | src |-+--| sink|
|_____|  | |_____|          |_____| |  |_____|
         |__________________________|

With this, you can now simulate any environment the Element might find itself in. By specifying the Caps of the harness Pads, using functions like set_src_caps or set_sink_caps_str, you can test how the Element interacts with different caps sets.

Your harnessed Element can of course also be a bin, and using gst_harness_new_parse supporting standard gst-launch syntax, you can easily test a whole pipeline instead of just one element.

You can then go on to push Buffers and Events on to the srcpad, using functions like push and push_event, and then pull them out to examine them with pull and pull_event.

typeof (unichar2) typeof (unichar2) A simple buffer-in buffer-out example

  #include <gst/gst.h>
  #include <gst/check/gstharness.h>
  GstHarness *h;
  GstBuffer *in_buf;
  GstBuffer *out_buf;

  // attach the harness to the src and sink pad of GstQueue
  h = gst_harness_new ("queue");

  // we must specify a caps before pushing buffers
  gst_harness_set_src_caps_str (h, "mycaps");

  // create a buffer of size 42
  in_buf = gst_harness_create_buffer (h, 42);

  // push the buffer into the queue
  gst_harness_push (h, in_buf);

  // pull the buffer from the queue
  out_buf = gst_harness_pull (h);

  // validate the buffer in is the same as buffer out
  fail_unless (in_buf == out_buf);

  // cleanup
  gst_buffer_unref (out_buf);
  gst_harness_teardown (h);

Another main feature of the Harness is its integration with the TestClock. Operating the TestClock can be very challenging, but Harness simplifies some of the most desired actions a lot, like wanting to manually advance the clock while at the same time releasing a ClockID that is waiting, with functions like crank_single_clock_wait.

Harness also supports sub-harnesses, as a way of generating and validating data. A sub-harness is another Harness that is managed by the "parent" harness, and can either be created by using the standard gst_harness_new type functions directly on the (GstHarness *)->src_harness, or using the much more convenient add_src or add_sink_parse. If you have a decoder-element you want to test, (like vp8dec) it can be very useful to add a src-harness with both a src-element (videotestsrc) and an encoder (vp8enc) to feed the decoder data with different configurations, by simply doing:

  GstHarness * h = gst_harness_new ("vp8dec");
  gst_harness_add_src_parse (h, "videotestsrc is-live=1 ! vp8enc", TRUE);

and then feeding it data with:

gst_harness_push_from_src (h);


Namespace: Gst.Check
Package: gstreamer-check-1.0

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