### Question:
Strings { public static String join(List<String> src, String delimiter) { return src == null ? null : String.join(delimiter, src.toArray(new String[0])); } private  Strings(); static String toCsv(List<String> src); static String join(List<String> src, String delimiter); static String capitaliseFirstLetter(String string); static String lowercaseFirstLetter(String string); static String zeros(int n); static String repeat(char value, int n); static boolean isEmpty(String s);  }### Answer:
@Test public void testJoin() { assertThat(join(Arrays.asList("a", "b"), "|"), is("a|b")); assertNull(join(null, "|")); assertThat(join(Collections.singletonList("a"), "|"), is("a")); }
@Test public void testJoin() { assertEquals(join(Arrays.asList("a", "b"), "|"), ("a|b")); assertNull(join(null, "|")); assertEquals(join(Collections.singletonList("a"), "|"), ("a")); }