@Test public void parse_emptyKeysNotOk() {

  for (String missingKey : Arrays.asList("=", "=v1", ",=", ",=v2")) {
    assertThatThrownBy(() -> entrySplitter.parse(parseIntoMap, map, missingKey))
        .isInstanceOf(IllegalArgumentException.class)
        .hasMessage("Invalid input: no key before '='");
  }
}