videotestsrc

 gst-launch-1.0 videotestsrc pattern=snow ! autovideosink 

smpte (0) snow (1) black (2) white (3) red (4) green (5) blue (6) checkers-1 (7) checkers-2 (8) checkers-4 (9) checkers-8 (10) circular (11) blink (12) smpte75 (13) zone-plate (14) gamut (15) chroma-zone-plate (16) solid-color (17) ball (18) smpte100 (19) bar (20) pinwheel (21) spokes (22) gradient (23) colors (24) smpte-rp-219 (25)