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testing-and-benchmarking
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Testing and Benchmarking</title>
<link rel=stylesheet href="site.css">
</head>
<script>
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<body>
<div class="example" id="testing-and-benchmarking">
<h2><a href="./">Go by Example</a>: Testing and Benchmarking</h2>
<table>
<tr>
<td class="docs">
<p>Unit testing is an important part of writing
principled Go programs. The <code>testing</code> package
provides the tools we need to write unit tests
and the <code>go test</code> command runs tests.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
<p>For the sake of demonstration, this code is in package
<code>main</code>, but it could be any package. Testing code
typically lives in the same package as the code it tests.</p>
</td>
<td class="code leading">
<a href="http://play.golang.org/p/PlzU16wwEWE"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma">
<span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="p">(</span>
<span class="s">"fmt"</span>
<span class="s">"testing"</span>
<span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>We’ll be testing this simple implementation of an
integer minimum. Typically, the code we’re testing
would be in a source file named something like
<code>intutils.go</code>, and the test file for it would then
be named <code>intutils_test.go</code>.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">IntMin</span><span class="p">(</span><span class="nx">a</span><span class="p">,</span> <span class="nx">b</span> <span class="kt">int</span><span class="p">)</span> <span class="kt">int</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">a</span> <span class="p"><</span> <span class="nx">b</span> <span class="p">{</span>
<span class="k">return</span> <span class="nx">a</span>
<span class="p">}</span>
<span class="k">return</span> <span class="nx">b</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>A test is created by writing a function with a name
beginning with <code>Test</code>.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">TestIntMinBasic</span><span class="p">(</span><span class="nx">t</span> <span class="o">*</span><span class="nx">testing</span><span class="p">.</span><span class="nx">T</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">ans</span> <span class="o">:=</span> <span class="nf">IntMin</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="o">-</span><span class="mi">2</span><span class="p">)</span>
<span class="k">if</span> <span class="nx">ans</span> <span class="o">!=</span> <span class="o">-</span><span class="mi">2</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>t.Error*</code> will report test failures but continue
executing the test. <code>t.Fatal*</code> will report test
failures and stop the test immediately.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">t</span><span class="p">.</span><span class="nf">Errorf</span><span class="p">(</span><span class="s">"IntMin(2, -2) = %d; want -2"</span><span class="p">,</span> <span class="nx">ans</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Writing tests can be repetitive, so it’s idiomatic to
use a <em>table-driven style</em>, where test inputs and
expected outputs are listed in a table and a single loop
walks over them and performs the test logic.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">TestIntMinTableDriven</span><span class="p">(</span><span class="nx">t</span> <span class="o">*</span><span class="nx">testing</span><span class="p">.</span><span class="nx">T</span><span class="p">)</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">tests</span> <span class="p">=</span> <span class="p">[]</span><span class="kd">struct</span> <span class="p">{</span>
<span class="nx">a</span><span class="p">,</span> <span class="nx">b</span> <span class="kt">int</span>
<span class="nx">want</span> <span class="kt">int</span>
<span class="p">}{</span>
<span class="p">{</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">},</span>
<span class="p">{</span><span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">},</span>
<span class="p">{</span><span class="mi">2</span><span class="p">,</span> <span class="o">-</span><span class="mi">2</span><span class="p">,</span> <span class="o">-</span><span class="mi">2</span><span class="p">},</span>
<span class="p">{</span><span class="mi">0</span><span class="p">,</span> <span class="o">-</span><span class="mi">1</span><span class="p">,</span> <span class="o">-</span><span class="mi">1</span><span class="p">},</span>
<span class="p">{</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="o">-</span><span class="mi">1</span><span class="p">},</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>t.Run enables running “subtests”, one for each
table entry. These are shown separately
when executing <code>go test -v</code>.</p>
</td>
<td class="code leading">
<pre class="chroma"> <span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">tt</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">tests</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nx">testname</span> <span class="o">:=</span> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Sprintf</span><span class="p">(</span><span class="s">"%d,%d"</span><span class="p">,</span> <span class="nx">tt</span><span class="p">.</span><span class="nx">a</span><span class="p">,</span> <span class="nx">tt</span><span class="p">.</span><span class="nx">b</span><span class="p">)</span>
<span class="nx">t</span><span class="p">.</span><span class="nf">Run</span><span class="p">(</span><span class="nx">testname</span><span class="p">,</span> <span class="kd">func</span><span class="p">(</span><span class="nx">t</span> <span class="o">*</span><span class="nx">testing</span><span class="p">.</span><span class="nx">T</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">ans</span> <span class="o">:=</span> <span class="nf">IntMin</span><span class="p">(</span><span class="nx">tt</span><span class="p">.</span><span class="nx">a</span><span class="p">,</span> <span class="nx">tt</span><span class="p">.</span><span class="nx">b</span><span class="p">)</span>
<span class="k">if</span> <span class="nx">ans</span> <span class="o">!=</span> <span class="nx">tt</span><span class="p">.</span><span class="nx">want</span> <span class="p">{</span>
<span class="nx">t</span><span class="p">.</span><span class="nf">Errorf</span><span class="p">(</span><span class="s">"got %d, want %d"</span><span class="p">,</span> <span class="nx">ans</span><span class="p">,</span> <span class="nx">tt</span><span class="p">.</span><span class="nx">want</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">})</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Benchmark tests typically go in <code>_test.go</code> files and are
named beginning with <code>Benchmark</code>. The <code>testing</code> runner
executes each benchmark function several times, increasing
<code>b.N</code> on each run until it collects a precise measurement.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">BenchmarkIntMin</span><span class="p">(</span><span class="nx">b</span> <span class="o">*</span><span class="nx">testing</span><span class="p">.</span><span class="nx">B</span><span class="p">)</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Typically the benchmark runs a function we’re
benchmarking in a loop <code>b.N</code> times.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="p"><</span> <span class="nx">b</span><span class="p">.</span><span class="nx">N</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
<span class="nf">IntMin</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>Run all tests in the current project in verbose mode.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> go test -v
<span class="go">== RUN TestIntMinBasic
</span><span class="go">--- PASS: TestIntMinBasic (0.00s)
</span><span class="go">=== RUN TestIntMinTableDriven
</span><span class="go">=== RUN TestIntMinTableDriven/0,1
</span><span class="go">=== RUN TestIntMinTableDriven/1,0
</span><span class="go">=== RUN TestIntMinTableDriven/2,-2
</span><span class="go">=== RUN TestIntMinTableDriven/0,-1
</span><span class="go">=== RUN TestIntMinTableDriven/-1,0
</span><span class="go">--- PASS: TestIntMinTableDriven (0.00s)
</span><span class="go"> --- PASS: TestIntMinTableDriven/0,1 (0.00s)
</span><span class="go"> --- PASS: TestIntMinTableDriven/1,0 (0.00s)
</span><span class="go"> --- PASS: TestIntMinTableDriven/2,-2 (0.00s)
</span><span class="go"> --- PASS: TestIntMinTableDriven/0,-1 (0.00s)
</span><span class="go"> --- PASS: TestIntMinTableDriven/-1,0 (0.00s)
</span><span class="go">PASS
</span><span class="go">ok examples/testing-and-benchmarking 0.023s</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Run all benchmarks in the current project. All tests
are run prior to benchmarks. The <code>bench</code> flag filters
benchmark function names with a regexp.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="gp">$</span> go test -bench=.
<span class="go">goos: darwin
</span><span class="go">goarch: arm64
</span><span class="go">pkg: examples/testing
</span><span class="go">BenchmarkIntMin-8 1000000000 0.3136 ns/op
</span><span class="go">PASS
</span><span class="go">ok examples/testing-and-benchmarking 0.351s</span></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="command-line-arguments">Command-Line Arguments</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
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