further to nervous's post on recommendations, this is from the buildings act which states builders cannot , for the sake of their margins, force a soil test down your throat if you have already gotten one done:
Part 3, S30, Paragraph 5 of the Domestic Building Contracts Act 1995, administered by Consumer Affairs Victoria, which states:
It is not necessary for a builder to commission the preparation of foundations data under this section to the extent that such data already exists and it is reasonable for the builder to rely on that data.