[lang-ref] ( add ) ( cpp )

TEST(SetOperation, Add) {
    // insert()
    set<int> s = { 1, 2, 3 };

    s.insert(4); // new elem
    s.insert(2); // already exists (no change)

    set<int> expected = { 1, 2, 3, 4 };
    EXPECT_EQ(s, expected);
}