Simple test fails

[smimram]

The script

output(video.testsrc())

fails at runtime with

2023/08/23 17:38:01 [clock.pulseaudio:2] Source pulse_out(liquidsoap:) failed while streaming: Invalid_argument("option is None")!
2023/08/23 17:38:01 [clock.pulseaudio:2] Raised at Stdlib.invalid_arg in file "stdlib.ml", line 30, characters 20-45
2023/08/23 17:38:01 [clock.pulseaudio:2] Called from Stdlib__Option.get in file "option.ml" (inlined), line 21, characters 41-69
2023/08/23 17:38:01 [clock.pulseaudio:2] Called from Source.operator#video_dimensions in file "src/core/source.ml", line 431, characters 8-92
2023/08/23 17:38:01 [clock.pulseaudio:2] Called from Video_testsrc.testsrc#synthesize in file "src/core/sources/video_testsrc.ml", line 42, characters 38-59
2023/08/23 17:38:01 [clock.pulseaudio:2] Called from Synthesized.source#get_frame in file "src/core/sources/synthesized.ml", line 60, characters 8-37
2023/08/23 17:38:01 [clock.pulseaudio:2] Called from Source.operator#instrumented_get_frame in file "src/core/source.ml", line 654, characters 6-24
2023/08/23 17:38:01 [clock.pulseaudio:2] Called from Source.operator#get in file "src/core/source.ml", line 764, characters 10-41
2023/08/23 17:38:01 [clock.pulseaudio:2] Called from Output.output#output in file "src/core/outputs/output.ml", line 173, characters 10-30
2023/08/23 17:38:01 [clock.pulseaudio:2] Called from Clock.MkClock.clock#end_tick.(fun) in file "src/core/clock.ml", line 318, characters 16-24