unittest.main()</code></pre>

<li>To write a test case, first subclass the <code>TestCase</code> class of the <code>unittest</code> module. This class provides many useful methods which you can use in your test case to test specific conditions.

<li>Every individual test is its own method. A test method takes no parameters, returns no value, and must have a name beginning with the four letters <code>test</code>. If a test method exits normally without raising an exception, the test is considered passed; if the method raises an exception, the test is considered failed.

<li>Here you call the actual <code>to_roman()</code> function. (Well, the function hasn&#8217;t been written yet, but once it is, this is the line that will call it.) Notice that you have now defined the <abbr>API</abbr> for the <code>to_roman()</code> function: it must take an integer (the number to convert) and return a string (the Roman numeral representation). If the <abbr>API</abbr> is different than that, this test is considered failed. Also notice that you are not trapping any exceptions when you call <code>to_roman()</code>. This is intentional. <code>to_roman()</code> shouldn&#8217;t raise an exception when you call it with valid input, and these input values are all valid. If <code>to_roman()</code> raises an exception, this test is considered failed.

<li>Assuming the <code>to_roman()</code> function was defined correctly, called correctly, completed successfully, and returned a value, the last step is to check whether it returned the <em>right</em> value. This is a common question, and the <code>TestCase</code> class provides a method, <code>assertEqual</code>, to check whether two values are equal. If the result returned from <code>to_roman()</code> (<var>result</var>) does not match the known value you were expecting (<var>numeral</var>), <code>assertEqual</code> will raise an exception and the test will fail. If the two values are equal, <code>assertEqual</code> will do nothing. If every value returned from <code>to_roman()</code> matches the known value you expect, <code>assertEqual</code> never raises an exception, so <code>test_to_roman_known_values</code> eventually exits normally, which means <code>to_roman()</code> has passed this test.