Here's a simple test for automating a Biquad filter. The main intent is have a fast automation to demonstrate a-rate automation, if available. Check the graph below to see if you have a-rate biquads.
This is based on the example from WebAudio issue #509. We have a 440-Hz sine-wave oscillator connected to a bandpass filter. The center frequency of the filter is 264 Hz. The center frequency of the filter is driven by another sine-wave oscillator with a frequency of 103 Hz with an amplitude of 148. This causes the center frequency of the bandpass filter to oscillate between 116 Hz to 412 Hz.
If only k-rate automation is supported, the output should be a little bit buzzy. With a-rate automation, the sound should be smooth.
Graph of the output of a 4400 Hz sine wave through a lowpass biquad filter with a cutoff frequency of 4400 Hz that is linear ramped from 4400 Hz to 10 Hz in 0.01 sec. If a-rate automation for the biquad is supported, the curve is nice and smooth. If note, you will see a stairstep curve with some possibly odd artifacts