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| 55 | <H2><A NAME="SECTION007410000000000000000"></A><A NAME="writing-tests"></A> |
| 56 | <BR> |
| 57 | 5.4.1 Writing Unit Tests for the <tt class="module">test</tt> package |
| 58 | </H2> |
| 59 | |
| 60 | <P> |
| 61 | It is preferred that tests for the <tt class="module">test</tt> package use the |
| 62 | <tt class="module"><a href="module-unittest.html">unittest</a></tt> module and follow a few guidelines. |
| 63 | One is to have the name of all the test methods start with "<tt class="samp">test_</tt>" as |
| 64 | well as the module's name. |
| 65 | This is needed so that the methods are recognized by the test driver as |
| 66 | test methods. |
| 67 | Also, no documentation string for the method should be included. |
| 68 | A comment (such as |
| 69 | "<tt class="samp"># Tests function returns only True or False</tt>") should be used to provide |
| 70 | documentation for test methods. |
| 71 | This is done because documentation strings get printed out if they exist and |
| 72 | thus what test is being run is not stated. |
| 73 | |
| 74 | <P> |
| 75 | A basic boilerplate is often used: |
| 76 | |
| 77 | <P> |
| 78 | <div class="verbatim"><pre> |
| 79 | import unittest |
| 80 | from test import test_support |
| 81 | |
| 82 | class MyTestCase1(unittest.TestCase): |
| 83 | |
| 84 | # Only use setUp() and tearDown() if necessary |
| 85 | |
| 86 | def setUp(self): |
| 87 | ... code to execute in preparation for tests ... |
| 88 | |
| 89 | def tearDown(self): |
| 90 | ... code to execute to clean up after tests ... |
| 91 | |
| 92 | def test_feature_one(self): |
| 93 | # Test feature one. |
| 94 | ... testing code ... |
| 95 | |
| 96 | def test_feature_two(self): |
| 97 | # Test feature two. |
| 98 | ... testing code ... |
| 99 | |
| 100 | ... more test methods ... |
| 101 | |
| 102 | class MyTestCase2(unittest.TestCase): |
| 103 | ... same structure as MyTestCase1 ... |
| 104 | |
| 105 | ... more test classes ... |
| 106 | |
| 107 | def test_main(): |
| 108 | test_support.run_unittest(MyTestCase1, |
| 109 | MyTestCase2, |
| 110 | ... list other tests ... |
| 111 | ) |
| 112 | |
| 113 | if __name__ == '__main__': |
| 114 | test_main() |
| 115 | </pre></div> |
| 116 | |
| 117 | <P> |
| 118 | This boilerplate code allows the testing suite to be run by |
| 119 | <tt class="module">test.regrtest</tt> as well as on its own as a script. |
| 120 | |
| 121 | <P> |
| 122 | The goal for regression testing is to try to break code. |
| 123 | This leads to a few guidelines to be followed: |
| 124 | |
| 125 | <P> |
| 126 | |
| 127 | <UL> |
| 128 | <LI>The testing suite should exercise all classes, functions, and |
| 129 | constants. |
| 130 | This includes not just the external API that is to be presented to the |
| 131 | outside world but also "private" code. |
| 132 | </LI> |
| 133 | <LI>Whitebox testing (examining the code being tested when the tests are |
| 134 | being written) is preferred. |
| 135 | Blackbox testing (testing only the published user interface) is not |
| 136 | complete enough to make sure all boundary and edge cases are tested. |
| 137 | </LI> |
| 138 | <LI>Make sure all possible values are tested including invalid ones. |
| 139 | This makes sure that not only all valid values are acceptable but also |
| 140 | that improper values are handled correctly. |
| 141 | </LI> |
| 142 | <LI>Exhaust as many code paths as possible. |
| 143 | Test where branching occurs and thus tailor input to make sure as many |
| 144 | different paths through the code are taken. |
| 145 | </LI> |
| 146 | <LI>Add an explicit test for any bugs discovered for the tested code. |
| 147 | This will make sure that the error does not crop up again if the code is |
| 148 | changed in the future. |
| 149 | </LI> |
| 150 | <LI>Make sure to clean up after your tests (such as close and remove all |
| 151 | temporary files). |
| 152 | </LI> |
| 153 | <LI>Import as few modules as possible and do it as soon as possible. |
| 154 | This minimizes external dependencies of tests and also minimizes possible |
| 155 | anomalous behavior from side-effects of importing a module. |
| 156 | </LI> |
| 157 | <LI>Try to maximize code reuse. |
| 158 | On occasion, tests will vary by something as small as what type |
| 159 | of input is used. |
| 160 | Minimize code duplication by subclassing a basic test class with a class |
| 161 | that specifies the input: |
| 162 | <div class="verbatim"><pre> |
| 163 | class TestFuncAcceptsSequences(unittest.TestCase): |
| 164 | |
| 165 | func = mySuperWhammyFunction |
| 166 | |
| 167 | def test_func(self): |
| 168 | self.func(self.arg) |
| 169 | |
| 170 | class AcceptLists(TestFuncAcceptsSequences): |
| 171 | arg = [1,2,3] |
| 172 | |
| 173 | class AcceptStrings(TestFuncAcceptsSequences): |
| 174 | arg = 'abc' |
| 175 | |
| 176 | class AcceptTuples(TestFuncAcceptsSequences): |
| 177 | arg = (1,2,3) |
| 178 | </pre></div> |
| 179 | </LI> |
| 180 | </UL> |
| 181 | |
| 182 | <P> |
| 183 | <div class="seealso"> |
| 184 | <p class="heading">See Also:</p> |
| 185 | |
| 186 | <dl compact="compact" class="seetitle"> |
| 187 | <dt><em class="citetitle" |
| 188 | >Test Driven Development</em></dt> |
| 189 | <dd>A book by Kent Beck on writing tests before code.</dd> |
| 190 | </dl> |
| 191 | </div> |
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| 229 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> |
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