Inspired by the book: “Shop Machines” by John White, I found that I could get excellent results with shop made fixtures. The only expensive thing to purchase is a good dial indicator.
Blade alignment on a table saw should be checked at three blade positions: 1) vertical at maximum height; 2) vertical at minimum height; 3) bevel 45 degrees at maximum height.
Some table saws, such as SawStop ICS, have separate adjustment for each of these alignments, but even on a saw without separate adjustments it is good to know what the alignment errors are.
Most instructions for alignment say to measure off of the blade. A better approach is to replace the blade with a rigid arm. I used 1/2 inch phenolic for the arm. An arm has two advantages, over a blade: 1) deviations on the dial gauge are amplified, which gives a better indication of the alignment error; 2) when the blade is at minimum height the arm still projects above the table so a standard dial gauge can still be used, whereas with a blade, a special vertical dial gauge would be required.
Photos below, Video here