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POUnit testing with generated inputs and expected outputs
 

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    <p>I'm writing some simple unit tests for a method which acts like a database query: it returns a list of results that can be customised using a limit (max of n results) and a page (the p'th set of n results). I'd like to test a few cases, such as:</p> <ul> <li>Return all the results</li> <li>Return the first page of a limited result set</li> <li>Return an aribtrary page of a limited result set</li> <li>Return the last page of a limited result set which overruns the total number of results</li> <li>Return a page beyond the total number of results</li> </ul> <p>I need to mock the results (effectively names) that are returned, so I'm just generating them with a counter to make a list of "Name #1", "Name #2", etc. for as many as I need. Each test looks (roughly) like:</p> <pre><code>public void testGetMockCandidatesLimited() throws Exception { int numResults = 4; setupMock(numResults); results = queryFunction(...); // Check that the expected number of results was returned assertEquals(numResults, results.size()); // Check that the results are correct and in order for (int i = 0; i &lt; numResults; i++) { assertEquals(result.get(i).getName(), "Name #" + (i + 1)); } } </code></pre> <p>My question is: is it okay to 'generate' the expected answers in this way? This is a trivial example, but the next step was to write a test to write a test to get the second page of two results each, and I had:</p> <pre><code> final int TEST_LIMIT = 2, TEST_PAGE = 1; // Check that the expected number of results was returned assertEquals(numResults, results.size()); // Check that the results are correct and in order for (int i = TEST_LIMIT * TEST_PAGE; i &lt; TEST_LIMIT * TEST_PAGE + TEST_LIMIT; i++) { assertEquals(result.get(i).getName(), "Name #" + (i + 1)); } </code></pre> <p>Now it just so happens that this test is 'correct' in the sense that i will take on the values that I expect it to and ensure that the results are "Name #3" and "Name #4". However it also happens that my queryFunction calculates which results to return in the same way (<code>limit * page + limit</code> kind of thing).</p> <p>This is concerning because if the test generates the expected answers in the same way that the unit under test does, it won't detect if there's a bug in that approach. However naming the input values with constants makes the tests much more readable than just have magic integers between 1 and 4 plugged in everywhere.</p> <p>What is the best way to deal with this situation, for both readability and maintainability (e.g. changing values in the future, should you need to)?</p>
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