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54 | <H2><A NAME="SECTION007280000000000000000"></A><A NAME="doctest-soapbox"></A> | |
55 | <BR> | |
56 | 5.2.8 Soapbox | |
57 | </H2> | |
58 | ||
59 | <P> | |
60 | As mentioned in the introduction, <tt class="module"><a href="module-doctest.html">doctest</a></tt> has grown to have | |
61 | three primary uses: | |
62 | ||
63 | <P> | |
64 | ||
65 | <OL> | |
66 | <LI>Checking examples in docstrings. | |
67 | </LI> | |
68 | <LI>Regression testing. | |
69 | </LI> | |
70 | <LI>Executable documentation / literate testing. | |
71 | </LI> | |
72 | </OL> | |
73 | ||
74 | <P> | |
75 | These uses have different requirements, and it is important to | |
76 | distinguish them. In particular, filling your docstrings with obscure | |
77 | test cases makes for bad documentation. | |
78 | ||
79 | <P> | |
80 | When writing a docstring, choose docstring examples with care. | |
81 | There's an art to this that needs to be learned--it may not be | |
82 | natural at first. Examples should add genuine value to the | |
83 | documentation. A good example can often be worth many words. | |
84 | If done with care, the examples will be invaluable for your users, and | |
85 | will pay back the time it takes to collect them many times over as the | |
86 | years go by and things change. I'm still amazed at how often one of | |
87 | my <tt class="module"><a href="module-doctest.html">doctest</a></tt> examples stops working after a "harmless" | |
88 | change. | |
89 | ||
90 | <P> | |
91 | Doctest also makes an excellent tool for regression testing, especially if | |
92 | you don't skimp on explanatory text. By interleaving prose and examples, | |
93 | it becomes much easier to keep track of what's actually being tested, and | |
94 | why. When a test fails, good prose can make it much easier to figure out | |
95 | what the problem is, and how it should be fixed. It's true that you could | |
96 | write extensive comments in code-based testing, but few programmers do. | |
97 | Many have found that using doctest approaches instead leads to much clearer | |
98 | tests. Perhaps this is simply because doctest makes writing prose a little | |
99 | easier than writing code, while writing comments in code is a little | |
100 | harder. I think it goes deeper than just that: the natural attitude | |
101 | when writing a doctest-based test is that you want to explain the fine | |
102 | points of your software, and illustrate them with examples. This in | |
103 | turn naturally leads to test files that start with the simplest features, | |
104 | and logically progress to complications and edge cases. A coherent | |
105 | narrative is the result, instead of a collection of isolated functions | |
106 | that test isolated bits of functionality seemingly at random. It's | |
107 | a different attitude, and produces different results, blurring the | |
108 | distinction between testing and explaining. | |
109 | ||
110 | <P> | |
111 | Regression testing is best confined to dedicated objects or files. There | |
112 | are several options for organizing tests: | |
113 | ||
114 | <P> | |
115 | ||
116 | <UL> | |
117 | <LI>Write text files containing test cases as interactive examples, | |
118 | and test the files using <tt class="function">testfile()</tt> or | |
119 | <tt class="function">DocFileSuite()</tt>. This is recommended, although is | |
120 | easiest to do for new projects, designed from the start to use | |
121 | doctest. | |
122 | </LI> | |
123 | <LI>Define functions named <code>_regrtest_<i>topic</i></code> that | |
124 | consist of single docstrings, containing test cases for the | |
125 | named topics. These functions can be included in the same file | |
126 | as the module, or separated out into a separate test file. | |
127 | </LI> | |
128 | <LI>Define a <code>__test__</code> dictionary mapping from regression test | |
129 | topics to docstrings containing test cases. | |
130 | </LI> | |
131 | </UL> | |
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164 | </div> | |
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167 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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