Shadows on the Koyukuk by Sidney Huntington (as told by Jim Rearden) has part of a chapter devoted to how the Koyukon Athabascans hunted grizzly bears with spears.
Here's my summary of how a spear handle was chosen and tested, from pages 169-170:
The spear handle was cut in July from a birch no more than 2.5” in diameter growing on level ground. Preferably it would be cut from a slow-growing birch near a river, shaded by spruce trees. The bark was required to be pinkish-brown with no loose bark. Small, clean horizontal lines were a sign of strength. The tree was cut about a foot up from the ground.
A test piece would be cut from above the section that was going to be used as a handle. An axe would be placed across the end and driven in a short way with a baton. If it didn't split then hard, dry spruce wedges were driven into the cut. If it still didn't split it was acceptable.
The pole would be placed in the fire with the bark on to harden it. After the bark was burned off it would hung in the shade to dry for many weeks. Then it would be hardened in the fire again.
The pole would then be beaten against a tree that had its bark removed in every way the hunter thought might possibly break it. After that it would be held over a fire to expand the wood. If even a hairline crack was revealed the pole would be discarded.
Shadows on the Koyukuk is a very good book. I would definitely recommend it, especially for people interested in bushcraft. It's not a bushcraft book, but a biography of someone who lived a bushcraft lifestyle. I'm not sure why the price on Amazon is so high, I'm pretty sure it sells for $15-20 locally.