What is the legal test for invalidating an election?

I also note that what is at issue on this application is not, as it was in the case of Haig v. Canada, whether or not persons will be permitted to vote. It is whether the test established by the legislature for determining if an election should be declared ‑ which establishes a balance between an individual’s right to vote and the integrity of the voting system, for the benefit of all ‑ has been met. When an the election is declared invalid, the persons affected have another opportunity to vote.