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FAQ: rearrange and expand the discussion of testing

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Rob Pike 2011-11-09 13:19:23 -08:00
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@ -350,26 +350,6 @@ errors are particularly important when the programmer seeing the errors is
not familiar with the code.
</p>
<p>
The same arguments apply to the use of <code>assert()</code> in test programs. Proper
error handling means letting other tests run after one has failed, so
that the person debugging the failure gets a complete picture of what is
wrong. It is more useful for a test to report that
<code>isPrime</code> gives the wrong answer for 2, 3, 5, and 7 (or for
2, 4, 8, and 16) than to report that <code>isPrime</code> gives the wrong
answer for 2 and therefore no more tests were run. The programmer who
triggers the test failure may not be familiar with the code that fails.
Time invested writing a good error message now pays off later when the
test breaks.
</p>
<p>
In testing, if the amount of extra code required to write
good errors seems repetitive and overwhelming, it might work better as a
table-driven test instead.
Go has excellent support for data structure literals.
</p>
<p>
We understand that this is a point of contention. There are many things in
the Go language and libraries that differ from modern practices, simply
@ -1196,6 +1176,45 @@ builds a test binary, and runs it.
<p>See the <a href="/doc/code.html">How to Write Go Code</a> document for more details.</p>
<h3 id="testing_framework">
Where is my favorite helper function for testing?</h3>
<p>
Go's standard <code>testing</code> package makes it easy to write unit tests, but it lacks
features provided in other language's testing frameworks such as assertion functions.
An <a href="#assertions">earlier section</a> of this document explained why Go
doesn't have assertions, and
the same arguments apply to the use of <code>assert</code> in tests.
Proper error handling means letting other tests run after one has failed, so
that the person debugging the failure gets a complete picture of what is
wrong. It is more useful for a test to report that
<code>isPrime</code> gives the wrong answer for 2, 3, 5, and 7 (or for
2, 4, 8, and 16) than to report that <code>isPrime</code> gives the wrong
answer for 2 and therefore no more tests were run. The programmer who
triggers the test failure may not be familiar with the code that fails.
Time invested writing a good error message now pays off later when the
test breaks.
</p>
<p>
A related point is that testing frameworks tend to develop into mini-languages
of their own, with conditionals and controls and printing mechanisms,
but Go already has all those capabilities; why recreate them?
We'd rather write tests in Go; it's one fewer language to learn and the
approach keeps the tests straightforward and easy to understand.
</p>
<p>
If the amount of extra code required to write
good errors seems repetitive and overwhelming, the test might work better if
table-driven, iterating over a list of inputs and outputs defined
in a data structure (Go has excellent support for data structure literals).
The work to write a good test and good error messages will then be amortized over many
test cases. The standard Go library is full of illustrative examples, such as in
<a href="http://golang.org/src/pkg/fmt/fmt_test.go">the formatting
tests for the <code>fmt</code> package</a>.
</p>
<h2 id="Implementation">Implementation</h2>