So let's add a test for the other feature we want, which is to count the number of characters in the file. Since analyze_text() is now supposed to return two values, we'll have it return a tuple with line count in the first position and character count in the second. Our new test looks like this:

# text_analyzer.py

class TextAnalysisTests(unittest.TestCase):
    . . .
    def test_character_count(self):
        "Check that the character count is correct."
        self.assertEqual(analyze_text(self.filename)[1], 131)

And it fails as expected:

% python text_analyzer.py
E..
======================================================================
ERROR: test_character_count (__main__.TextAnalysisTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "text_analyzer.py", line 32, in test_character_count
    self.assertEqual(analyze_text(self.filename)[1], 131)
TypeError: 'int' object has no attribute '__getitem__'

----------------------------------------------------------------------
Ran 3 tests in 0.004s

FAILED (errors=1)

This result is telling us that it can't index into the integer returned by analyze_text(). So let's fix analyze_text() to return the proper tuple:

# text_analyzer.py

def analyze_text(filename):
    """Calculate the number of lines and characters in a file.

    Args:
      filename: The name of the file to analyze.

    Raises:
      IOError: If ``filename`` does not exist or can't be read.

    Returns: A tuple where the first element is the number of lines in
      the files and the second element is the number of characters.

    """
    lines = 0
    chars = 0
    with open(filename, 'r') as f:
        for line in f:
            lines += 1
            chars += len(line)
    return (lines, chars)

This fixes our new test, but we find we've broken an old one:

% python text_analyzer.py
..F
======================================================================
FAIL: test_line_count (__main__.TextAnalysisTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "text_analyzer.py", line 34, in test_line_count
    self.assertEqual(analyze_text(self.filename), 4)
AssertionError: (4, 131) != 4

----------------------------------------------------------------------
Ran 3 tests in 0.004s

FAILED (failures=1)

Fortunately that's easy enough to fix because all we need to do is account for the new return type in our earlier test:

# text_analyzer.py

class TextAnalysisTests(unittest.TestCase):
    . . .
    def test_line_count(self):
        "Check that the line count is correct."
        self.assertEqual(analyze_text(self.filename)[0], 4)

Now everything is passing again:

% python text_analyzer.py
...
----------------------------------------------------------------------
Ran 3 tests in 0.004s

OK