Test: Replace t.error/fatal with assert/request in [raft_paper_test.go]

[MrDXY]

Refactor: Replacing t.Error/t.Fatal with assert/require

This commit tries to eliminate boilerplate code in the testing suite by replacing occurrences
of t.Error and t.Fatal with assertions from the assert and require packages.

Changes Made:

• Replaced instances of t.Error with assert
• Replaced instances of t.Fatal with require

Affected Files:

• [raft_paper_test.go]

Part of: #146

[pav-kv]

LGTM % some suggestions

[pav-kv]

For another PR: consider removing messageSlice, and using slices.SortFunc with some stable comparator.

[MrDXY]

Would this be what you had in mind?

slices.SortStableFunc(data, orderMessageAsc)
func sortMessageAsc(a pb.Message, b pb.Message) int {
	strA := fmt.Sprint(a)
	strB := fmt.Sprint(b)
	if strA > strB {
		return 1
	} else if strA < strB {
		return -1
	} else {
		return 0
	}
}

[ahrtr]

lgtm

Thanks