The BBC article InSight Diary: The silence of space tells an interesting story and has an interesting audio recording of InSight's seismometer signals sped up to audio frequency, made while in presumably silent deep space on its way to Mars. Mysterious vibrations/sounds were recorded, and the article tells the story of their surprising discovery and mystery. It's worth the read.
These vibrations were detected in the two horizontal directions, by SP2 and SP3. Vertically oriented SP1 can not measure in microgravity because the Mars gravity-cancelling spring has no gravity to compensate it and so pushes the accelerometer to its limit.
If zero acceleration is too far out of the range of Mars' 3.71 m/s^2 acceleration, then Earth's 9.81 m/s^2 gravity would be way too large to test this accelerometer.
Question: Was the full 3D seismometer tested in Earth's gravity somehow? Perhaps dropped off the side of a building with a tether to simulate 0.38 g acceleration?
below: One of the microseismometer sensors, carved from a single piece of silicon 25mm square. Source