@Test
public void testConcatWithStrings() {

    assertEquals(concatWithString(" ", new String[]{"hello", "world"}), "hello world");
    assertEquals(concatWithString("  ", new String[]{"hello", "world"}), "hello  world");
    assertEquals(concatWithString("  ", new String[]{"", "world"}), "  world");
    assertEquals(concatWithString("-", new String[]{"hello", "world", "!"}), "hello-world-!");
    assertEquals(concatWithString("-", new String[]{}), "");
    assertEquals(concatWithString("-", new String[]{"hello"}), "hello");
}