google test: Use ASSERT_* instead of EXPECT_*. (#5765)

google test: Use ASSERT_* instead of EXPECT_*. (#5765)

Use ASSERT instead of EXPECT for consistency. There's no real benefit
for us to use EXPECT -- the main difference is that within a test,
EXPECT failures do not terminate the test, while ASSERT failures do.

This further fixes a minor issue in theory_sets_type_rules_white.h
(which is still not migrated to google test yet).