assertExpectedString(string);
  }

  public void testReadFirstLine() throws IOException {
    if (expectedLines.isEmpty()) {
      assertThat(source.readFirstLine()).isNull();
    } else {
      assertEquals(expectedLines.get(0), source.readFirstLine());
    }
  }

  public void testReadLines_toList() throws IOException {
    assertExpectedLines(source.readLines());
  }

    File temp = createTempFile();
    assertThat(Files.readFirstLine(temp, UTF_8)).isNull();
    assertTrue(Files.readLines(temp, UTF_8).isEmpty());

    PrintWriter w = new PrintWriter(Files.newWriter(temp, UTF_8));
    w.println("hello");
    w.println("");
    w.println(" world  ");
    w.println("");
    w.close();

    assertEquals("hello", Files.readFirstLine(temp, UTF_8));

    File temp = createTempFile();
    assertThat(Files.readFirstLine(temp, UTF_8)).isNull();
    assertTrue(Files.readLines(temp, UTF_8).isEmpty());

    PrintWriter w = new PrintWriter(Files.newWriter(temp, UTF_8));
    w.println("hello");
    w.println("");
    w.println(" world  ");
    w.println("");
    w.close();

    assertEquals("hello", Files.readFirstLine(temp, UTF_8));