Migrate code base to use "github.com/stretchr/testify/assert"

[ccaraman]

Currently there are parts of the code base that still use the pattern

if <some property> != <expected property> {
  t.Fatalf("...")
}

Migrate these instances to use
assert.* in place of this pattern.

[pjanotti]

It doesn't need to be done all at once, PRs doing it partially are helpful.

[huikang]

Hi, @ccaraman @pjanotti , I'd like to try working on this issue. If no one has taken it, please assign it to me. Thanks.

[tigrannajaryan]

@huikang assigned to you, thank you.

[ccaraman]

@huikang Let us know if you have any questions!