ImmutableList.Builder<String> builder = ImmutableList.builder();
    source.forEachLine(builder::add);
    assertExpectedLines(builder.build());
  }

  private void assertExpectedString(String string) {
    assertThat(string).isEqualTo(expected);
  }

  private void assertExpectedLines(List<String> list) {
    assertEquals(expectedLines, list);
  }