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FAQ: rearrange and expand the discussion of testing
R=gri, r, bradfitz, rsc CC=golang-dev https://golang.org/cl/5369052
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@ -350,26 +350,6 @@ errors are particularly important when the programmer seeing the errors is
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not familiar with the code.
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</p>
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<p>
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The same arguments apply to the use of <code>assert()</code> in test programs. Proper
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error handling means letting other tests run after one has failed, so
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that the person debugging the failure gets a complete picture of what is
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wrong. It is more useful for a test to report that
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<code>isPrime</code> gives the wrong answer for 2, 3, 5, and 7 (or for
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2, 4, 8, and 16) than to report that <code>isPrime</code> gives the wrong
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answer for 2 and therefore no more tests were run. The programmer who
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triggers the test failure may not be familiar with the code that fails.
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Time invested writing a good error message now pays off later when the
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test breaks.
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</p>
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<p>
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In testing, if the amount of extra code required to write
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good errors seems repetitive and overwhelming, it might work better as a
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table-driven test instead.
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Go has excellent support for data structure literals.
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</p>
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<p>
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We understand that this is a point of contention. There are many things in
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the Go language and libraries that differ from modern practices, simply
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@ -1196,6 +1176,45 @@ builds a test binary, and runs it.
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<p>See the <a href="/doc/code.html">How to Write Go Code</a> document for more details.</p>
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<h3 id="testing_framework">
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Where is my favorite helper function for testing?</h3>
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<p>
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Go's standard <code>testing</code> package makes it easy to write unit tests, but it lacks
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features provided in other language's testing frameworks such as assertion functions.
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An <a href="#assertions">earlier section</a> of this document explained why Go
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doesn't have assertions, and
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the same arguments apply to the use of <code>assert</code> in tests.
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Proper error handling means letting other tests run after one has failed, so
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that the person debugging the failure gets a complete picture of what is
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wrong. It is more useful for a test to report that
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<code>isPrime</code> gives the wrong answer for 2, 3, 5, and 7 (or for
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2, 4, 8, and 16) than to report that <code>isPrime</code> gives the wrong
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answer for 2 and therefore no more tests were run. The programmer who
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triggers the test failure may not be familiar with the code that fails.
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Time invested writing a good error message now pays off later when the
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test breaks.
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</p>
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<p>
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A related point is that testing frameworks tend to develop into mini-languages
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of their own, with conditionals and controls and printing mechanisms,
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but Go already has all those capabilities; why recreate them?
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We'd rather write tests in Go; it's one fewer language to learn and the
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approach keeps the tests straightforward and easy to understand.
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</p>
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<p>
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If the amount of extra code required to write
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good errors seems repetitive and overwhelming, the test might work better if
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table-driven, iterating over a list of inputs and outputs defined
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in a data structure (Go has excellent support for data structure literals).
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The work to write a good test and good error messages will then be amortized over many
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test cases. The standard Go library is full of illustrative examples, such as in
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<a href="http://golang.org/src/pkg/fmt/fmt_test.go">the formatting
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tests for the <code>fmt</code> package</a>.
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</p>
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<h2 id="Implementation">Implementation</h2>
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