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Hana 9e216da9ef go.mod: add go.mod and move pygments to third_party 
After go1.16, go will use module mode by default,
even when the repository is checked out under GOPATH
or in a one-off directory. Add go.mod, go.sum to keep
this repo buildable without opting out of the module
mode.

> go mod init github.com/mmcgrana/gobyexample
> go mod tidy
> go mod vendor

In module mode, the 'vendor' directory is special
and its contents will be actively maintained by the
go command. pygments aren't the dependency the go will
know about, so it will delete the contents from vendor
directory. Move it to `third_party` directory now.

And, vendor the blackfriday package.

Note: the tutorial contents are not affected by the
change in go1.16 because all the examples in this
tutorial ask users to run the go command with the
explicit list of files to be compiled (e.g.
`go run hello-world.go` or `go build command-line-arguments.go`).
When the source list is provided, the go command does
not have to compute the build list and whether it's
running in GOPATH mode or module mode becomes irrelevant.
2021-02-15 16:45:26 -05:00

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<!DOCTYPE html>
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<title>Go by Example: Testing</title>
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<body>
<div class="example" id="testing">
<h2><a href="./">Go by Example</a>: Testing</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/vY8PN0c6BSx"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
<span class="s">&quot;fmt&quot;</span>
<span class="s">&quot;testing&quot;</span>
<span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>We&rsquo;ll be testing this simple implementation of an
integer minimum. Typically, the code we&rsquo;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">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">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">&lt;</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></div>
</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">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">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="nx">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></div>
</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">
<div class="highlight"><pre> <span class="nx">t</span><span class="p">.</span><span class="nx">Errorf</span><span class="p">(</span><span class="s">&quot;IntMin(2, -2) = %d; want -2&quot;</span><span class="p">,</span> <span class="nx">ans</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Writing tests can be repetitive, so it&rsquo;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">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">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></div>
</td>
</tr>
<tr>
<td class="docs">
<p>t.Run enables running &ldquo;subtests&rdquo;, one for each
table entry. These are shown separately
when executing <code>go test -v</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <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></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">testname</span> <span class="o">:=</span> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Sprintf</span><span class="p">(</span><span class="s">&quot;%d,%d&quot;</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="nx">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="nx">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="nx">Errorf</span><span class="p">(</span><span class="s">&quot;got %d, want %d&quot;</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></div>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>Run all tests in the current project in verbose mode.</p>
</td>
<td class="code">
<div class="highlight"><pre><span class="gp">$</span> go <span class="nb">test</span> -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 0.023s</span>
</pre></div>
</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> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/testing">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
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