This will set the harnessed #GstElement to gst.types.State.Playing.
#GstElements without a sink-#GstPad and with the gst.types.ElementFlags.Source
flag set is considered a src #GstElement
Non-src #GstElements (like sinks and filters) are automatically set to
playing by the #GstHarness, but src #GstElements are not to avoid them
starting to produce buffers.
Hence, for src #GstElement you must call gstcheck.harness.Harness.play explicitly.
This will set the harnessed #GstElement to gst.types.State.Playing. #GstElements without a sink-#GstPad and with the gst.types.ElementFlags.Source flag set is considered a src #GstElement Non-src #GstElements (like sinks and filters) are automatically set to playing by the #GstHarness, but src #GstElements are not to avoid them starting to produce buffers. Hence, for src #GstElement you must call gstcheck.harness.Harness.play explicitly.
MT safe.