public void ReplaceStuff() {
Assert.AreEqual("abc abc qwe ab", "abc abc abc ab".ReplaceLastOccurrence("abc", "qwe"));
Assert.AreEqual("abc abc abc qwe", "abc abc abc ab".ReplaceLastOccurrence("ab", "qwe"));
Assert.AreEqual("abc abc abc ab", "abc abc abc ab".ReplaceLastOccurrence("abcd", "qwe"));
}
}