/usr/share/doc/python-hypothesis/html/quickstart.html is in python-hypothesis-doc 3.44.1-2ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 | <!DOCTYPE html>
<!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]-->
<!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]-->
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Quick start guide — Hypothesis 3.44.1 documentation</title>
<link rel="stylesheet" href="_static/css/theme.css" type="text/css" />
<link rel="index" title="Index"
href="genindex.html"/>
<link rel="search" title="Search" href="search.html"/>
<link rel="top" title="Hypothesis 3.44.1 documentation" href="index.html"/>
<link rel="next" title="Details and advanced features" href="details.html"/>
<link rel="prev" title="Welcome to Hypothesis!" href="index.html"/>
<script src="_static/js/modernizr.min.js"></script>
</head>
<body class="wy-body-for-nav" role="document">
<div class="wy-grid-for-nav">
<nav data-toggle="wy-nav-shift" class="wy-nav-side">
<div class="wy-side-scroll">
<div class="wy-side-nav-search">
<a href="index.html" class="icon icon-home"> Hypothesis
</a>
<div class="version">
3.44.1
</div>
<div role="search">
<form id="rtd-search-form" class="wy-form" action="search.html" method="get">
<input type="text" name="q" placeholder="Search docs" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
</div>
<div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation">
<ul class="current">
<li class="toctree-l1 current"><a class="current reference internal" href="#">Quick start guide</a><ul>
<li class="toctree-l2"><a class="reference internal" href="#an-example">An example</a></li>
<li class="toctree-l2"><a class="reference internal" href="#installing">Installing</a></li>
<li class="toctree-l2"><a class="reference internal" href="#running-tests">Running tests</a></li>
<li class="toctree-l2"><a class="reference internal" href="#writing-tests">Writing tests</a></li>
<li class="toctree-l2"><a class="reference internal" href="#where-to-start">Where to start</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="details.html">Details and advanced features</a></li>
<li class="toctree-l1"><a class="reference internal" href="settings.html">Settings</a></li>
<li class="toctree-l1"><a class="reference internal" href="data.html">What you can generate and how</a></li>
<li class="toctree-l1"><a class="reference internal" href="extras.html">Additional packages</a></li>
<li class="toctree-l1"><a class="reference internal" href="django.html">Hypothesis for Django users</a></li>
<li class="toctree-l1"><a class="reference internal" href="numpy.html">Hypothesis for the Scientific Stack</a></li>
<li class="toctree-l1"><a class="reference internal" href="healthchecks.html">Health checks</a></li>
<li class="toctree-l1"><a class="reference internal" href="database.html">The Hypothesis Example Database</a></li>
<li class="toctree-l1"><a class="reference internal" href="stateful.html">Stateful testing</a></li>
<li class="toctree-l1"><a class="reference internal" href="supported.html">Compatibility</a></li>
<li class="toctree-l1"><a class="reference internal" href="examples.html">Some more examples</a></li>
<li class="toctree-l1"><a class="reference internal" href="community.html">Community</a></li>
<li class="toctree-l1"><a class="reference internal" href="manifesto.html">The Purpose of Hypothesis</a></li>
<li class="toctree-l1"><a class="reference internal" href="endorsements.html">Testimonials</a></li>
<li class="toctree-l1"><a class="reference internal" href="usage.html">Open Source Projects using Hypothesis</a></li>
<li class="toctree-l1"><a class="reference internal" href="strategies.html">Projects extending Hypothesis</a></li>
<li class="toctree-l1"><a class="reference internal" href="changes.html">Changelog</a></li>
<li class="toctree-l1"><a class="reference internal" href="development.html">Ongoing Hypothesis Development</a></li>
<li class="toctree-l1"><a class="reference internal" href="support.html">Help and Support</a></li>
<li class="toctree-l1"><a class="reference internal" href="packaging.html">Packaging Guidelines</a></li>
<li class="toctree-l1"><a class="reference internal" href="reproducing.html">Reproducing Failures</a></li>
</ul>
</div>
</div>
</nav>
<section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">
<nav class="wy-nav-top" role="navigation" aria-label="top navigation">
<i data-toggle="wy-nav-top" class="fa fa-bars"></i>
<a href="index.html">Hypothesis</a>
</nav>
<div class="wy-nav-content">
<div class="rst-content">
<div role="navigation" aria-label="breadcrumbs navigation">
<ul class="wy-breadcrumbs">
<li><a href="index.html">Docs</a> »</li>
<li>Quick start guide</li>
<li class="wy-breadcrumbs-aside">
<a href="_sources/quickstart.rst.txt" rel="nofollow"> View page source</a>
</li>
</ul>
<hr/>
</div>
<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
<div itemprop="articleBody">
<div class="section" id="quick-start-guide">
<h1>Quick start guide<a class="headerlink" href="#quick-start-guide" title="Permalink to this headline">¶</a></h1>
<p>This document should talk you through everything you need to get started with
Hypothesis.</p>
<div class="section" id="an-example">
<h2>An example<a class="headerlink" href="#an-example" title="Permalink to this headline">¶</a></h2>
<p>Suppose we’ve written a <a class="reference external" href="https://en.wikipedia.org/wiki/Run-length_encoding">run length encoding</a> system and we want to test
it out.</p>
<p>We have the following code which I took straight from the
<a class="reference external" href="http://rosettacode.org/wiki/Run-length_encoding">Rosetta Code</a> wiki (OK, I
removed some commented out code and fixed the formatting, but there are no
functional modifications):</p>
<div class="code python highlight-default"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">encode</span><span class="p">(</span><span class="n">input_string</span><span class="p">):</span>
<span class="n">count</span> <span class="o">=</span> <span class="mi">1</span>
<span class="n">prev</span> <span class="o">=</span> <span class="s1">''</span>
<span class="n">lst</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">character</span> <span class="ow">in</span> <span class="n">input_string</span><span class="p">:</span>
<span class="k">if</span> <span class="n">character</span> <span class="o">!=</span> <span class="n">prev</span><span class="p">:</span>
<span class="k">if</span> <span class="n">prev</span><span class="p">:</span>
<span class="n">entry</span> <span class="o">=</span> <span class="p">(</span><span class="n">prev</span><span class="p">,</span> <span class="n">count</span><span class="p">)</span>
<span class="n">lst</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">entry</span><span class="p">)</span>
<span class="n">count</span> <span class="o">=</span> <span class="mi">1</span>
<span class="n">prev</span> <span class="o">=</span> <span class="n">character</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">count</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">entry</span> <span class="o">=</span> <span class="p">(</span><span class="n">character</span><span class="p">,</span> <span class="n">count</span><span class="p">)</span>
<span class="n">lst</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">entry</span><span class="p">)</span>
<span class="k">return</span> <span class="n">lst</span>
<span class="k">def</span> <span class="nf">decode</span><span class="p">(</span><span class="n">lst</span><span class="p">):</span>
<span class="n">q</span> <span class="o">=</span> <span class="s1">''</span>
<span class="k">for</span> <span class="n">character</span><span class="p">,</span> <span class="n">count</span> <span class="ow">in</span> <span class="n">lst</span><span class="p">:</span>
<span class="n">q</span> <span class="o">+=</span> <span class="n">character</span> <span class="o">*</span> <span class="n">count</span>
<span class="k">return</span> <span class="n">q</span>
</pre></div>
</div>
<p>We want to write a test for this that will check some invariant of these
functions.</p>
<p>The invariant one tends to try when you’ve got this sort of encoding /
decoding is that if you encode something and then decode it then you get the same
value back.</p>
<p>Lets see how you’d do that with Hypothesis:</p>
<div class="code python highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">hypothesis</span> <span class="k">import</span> <span class="n">given</span>
<span class="kn">from</span> <span class="nn">hypothesis.strategies</span> <span class="k">import</span> <span class="n">text</span>
<span class="nd">@given</span><span class="p">(</span><span class="n">text</span><span class="p">())</span>
<span class="k">def</span> <span class="nf">test_decode_inverts_encode</span><span class="p">(</span><span class="n">s</span><span class="p">):</span>
<span class="k">assert</span> <span class="n">decode</span><span class="p">(</span><span class="n">encode</span><span class="p">(</span><span class="n">s</span><span class="p">))</span> <span class="o">==</span> <span class="n">s</span>
</pre></div>
</div>
<p>(For this example we’ll just let pytest discover and run the test. We’ll cover
other ways you could have run it later).</p>
<p>The text function returns what Hypothesis calls a search strategy. An object
with methods that describe how to generate and simplify certain kinds of
values. The @given decorator then takes our test function and turns it into a
parametrized one which, when called, will run the test function over a wide
range of matching data from that strategy.</p>
<p>Anyway, this test immediately finds a bug in the code:</p>
<div class="code highlight-default"><div class="highlight"><pre><span></span><span class="n">Falsifying</span> <span class="n">example</span><span class="p">:</span> <span class="n">test_decode_inverts_encode</span><span class="p">(</span><span class="n">s</span><span class="o">=</span><span class="s1">''</span><span class="p">)</span>
<span class="ne">UnboundLocalError</span><span class="p">:</span> <span class="n">local</span> <span class="n">variable</span> <span class="s1">'character'</span> <span class="n">referenced</span> <span class="n">before</span> <span class="n">assignment</span>
</pre></div>
</div>
<p>Hypothesis correctly points out that this code is simply wrong if called on
an empty string.</p>
<p>If we fix that by just adding the following code to the beginning of the function
then Hypothesis tells us the code is correct (by doing nothing as you’d expect
a passing test to).</p>
<div class="code python highlight-default"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="ow">not</span> <span class="n">input_string</span><span class="p">:</span>
<span class="k">return</span> <span class="p">[]</span>
</pre></div>
</div>
<p>If we wanted to make sure this example was always checked we could add it in
explicitly:</p>
<div class="code python highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">hypothesis</span> <span class="k">import</span> <span class="n">given</span><span class="p">,</span> <span class="n">example</span>
<span class="kn">from</span> <span class="nn">hypothesis.strategies</span> <span class="k">import</span> <span class="n">text</span>
<span class="nd">@given</span><span class="p">(</span><span class="n">text</span><span class="p">())</span>
<span class="nd">@example</span><span class="p">(</span><span class="s1">''</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">test_decode_inverts_encode</span><span class="p">(</span><span class="n">s</span><span class="p">):</span>
<span class="k">assert</span> <span class="n">decode</span><span class="p">(</span><span class="n">encode</span><span class="p">(</span><span class="n">s</span><span class="p">))</span> <span class="o">==</span> <span class="n">s</span>
</pre></div>
</div>
<p>You don’t have to do this, but it can be useful both for clarity purposes and
for reliably hitting hard to find examples. Also in local development
Hypothesis will just remember and reuse the examples anyway, but there’s not
currently a very good workflow for sharing those in your CI.</p>
<p>It’s also worth noting that both example and given support keyword arguments as
well as positional. The following would have worked just as well:</p>
<div class="code python highlight-default"><div class="highlight"><pre><span></span><span class="nd">@given</span><span class="p">(</span><span class="n">s</span><span class="o">=</span><span class="n">text</span><span class="p">())</span>
<span class="nd">@example</span><span class="p">(</span><span class="n">s</span><span class="o">=</span><span class="s1">''</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">test_decode_inverts_encode</span><span class="p">(</span><span class="n">s</span><span class="p">):</span>
<span class="k">assert</span> <span class="n">decode</span><span class="p">(</span><span class="n">encode</span><span class="p">(</span><span class="n">s</span><span class="p">))</span> <span class="o">==</span> <span class="n">s</span>
</pre></div>
</div>
<p>Suppose we had a more interesting bug and forgot to reset the count
each time. Say we missed a line in our <code class="docutils literal"><span class="pre">encode</span></code> method:</p>
<div class="code python highlight-default"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">encode</span><span class="p">(</span><span class="n">input_string</span><span class="p">):</span>
<span class="n">count</span> <span class="o">=</span> <span class="mi">1</span>
<span class="n">prev</span> <span class="o">=</span> <span class="s1">''</span>
<span class="n">lst</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">character</span> <span class="ow">in</span> <span class="n">input_string</span><span class="p">:</span>
<span class="k">if</span> <span class="n">character</span> <span class="o">!=</span> <span class="n">prev</span><span class="p">:</span>
<span class="k">if</span> <span class="n">prev</span><span class="p">:</span>
<span class="n">entry</span> <span class="o">=</span> <span class="p">(</span><span class="n">prev</span><span class="p">,</span> <span class="n">count</span><span class="p">)</span>
<span class="n">lst</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">entry</span><span class="p">)</span>
<span class="c1"># count = 1 # Missing reset operation</span>
<span class="n">prev</span> <span class="o">=</span> <span class="n">character</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">count</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">entry</span> <span class="o">=</span> <span class="p">(</span><span class="n">character</span><span class="p">,</span> <span class="n">count</span><span class="p">)</span>
<span class="n">lst</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">entry</span><span class="p">)</span>
<span class="k">return</span> <span class="n">lst</span>
</pre></div>
</div>
<p>Hypothesis quickly informs us of the following example:</p>
<div class="code highlight-default"><div class="highlight"><pre><span></span><span class="n">Falsifying</span> <span class="n">example</span><span class="p">:</span> <span class="n">test_decode_inverts_encode</span><span class="p">(</span><span class="n">s</span><span class="o">=</span><span class="s1">'001'</span><span class="p">)</span>
</pre></div>
</div>
<p>Note that the example provided is really quite simple. Hypothesis doesn’t just
find <em>any</em> counter-example to your tests, it knows how to simplify the examples
it finds to produce small easy to understand ones. In this case, two identical
values are enough to set the count to a number different from one, followed by
another distinct value which should have reset the count but in this case
didn’t.</p>
<p>The examples Hypothesis provides are valid Python code you can run. Any
arguments that you explicitly provide when calling the function are not
generated by Hypothesis, and if you explicitly provide <em>all</em> the arguments
Hypothesis will just call the underlying function the once rather than
running it multiple times.</p>
</div>
<div class="section" id="installing">
<h2>Installing<a class="headerlink" href="#installing" title="Permalink to this headline">¶</a></h2>
<p>Hypothesis is <a class="reference external" href="https://pypi.python.org/pypi/hypothesis">available on pypi as “hypothesis”</a>. You can install it with:</p>
<div class="code bash highlight-default"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="n">hypothesis</span>
</pre></div>
</div>
<p>If you want to install directly from the source code (e.g. because you want to
make changes and install the changed version) you can do this with:</p>
<div class="code bash highlight-default"><div class="highlight"><pre><span></span><span class="n">pip</span> <span class="n">install</span> <span class="o">-</span><span class="n">e</span> <span class="o">.</span>
</pre></div>
</div>
<p>You should probably run the tests first to make sure nothing is broken. You can
do this with:</p>
<div class="code bash highlight-default"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="n">setup</span><span class="o">.</span><span class="n">py</span> <span class="n">test</span>
</pre></div>
</div>
<p>Note that if they’re not already installed this will try to install the test
dependencies.</p>
<p>You may wish to do all of this in a <a class="reference external" href="https://virtualenv.pypa.io/en/latest/">virtualenv</a>. For example:</p>
<div class="code bash highlight-default"><div class="highlight"><pre><span></span><span class="n">virtualenv</span> <span class="n">venv</span>
<span class="n">source</span> <span class="n">venv</span><span class="o">/</span><span class="nb">bin</span><span class="o">/</span><span class="n">activate</span>
<span class="n">pip</span> <span class="n">install</span> <span class="n">hypothesis</span>
</pre></div>
</div>
<p>Will create an isolated environment for you to try hypothesis out in without
affecting your system installed packages.</p>
</div>
<div class="section" id="running-tests">
<h2>Running tests<a class="headerlink" href="#running-tests" title="Permalink to this headline">¶</a></h2>
<p>In our example above we just let pytest discover and run our tests, but we could
also have run it explicitly ourselves:</p>
<div class="code python highlight-default"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span>
<span class="n">test_decode_inverts_encode</span><span class="p">()</span>
</pre></div>
</div>
<p>We could also have done this as a unittest TestCase:</p>
<div class="code python highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">unittest</span>
<span class="k">class</span> <span class="nc">TestEncoding</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>
<span class="nd">@given</span><span class="p">(</span><span class="n">text</span><span class="p">())</span>
<span class="k">def</span> <span class="nf">test_decode_inverts_encode</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">s</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">assertEqual</span><span class="p">(</span><span class="n">decode</span><span class="p">(</span><span class="n">encode</span><span class="p">(</span><span class="n">s</span><span class="p">)),</span> <span class="n">s</span><span class="p">)</span>
<span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span>
<span class="n">unittest</span><span class="o">.</span><span class="n">main</span><span class="p">()</span>
</pre></div>
</div>
<p>A detail: This works because Hypothesis ignores any arguments it hasn’t been
told to provide (positional arguments start from the right), so the self
argument to the test is simply ignored and works as normal. This also means
that Hypothesis will play nicely with other ways of parameterizing tests. e.g
it works fine if you use pytest fixtures for some arguments and Hypothesis for
others.</p>
</div>
<div class="section" id="writing-tests">
<h2>Writing tests<a class="headerlink" href="#writing-tests" title="Permalink to this headline">¶</a></h2>
<p>A test in Hypothesis consists of two parts: A function that looks like a normal
test in your test framework of choice but with some additional arguments, and
a <a class="reference internal" href="details.html#hypothesis.given" title="hypothesis.given"><code class="xref py py-func docutils literal"><span class="pre">@given</span></code></a> decorator that specifies
how to provide those arguments.</p>
<p>Here are some other examples of how you could use that:</p>
<div class="code python highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">hypothesis</span> <span class="k">import</span> <span class="n">given</span>
<span class="kn">import</span> <span class="nn">hypothesis.strategies</span> <span class="k">as</span> <span class="nn">st</span>
<span class="nd">@given</span><span class="p">(</span><span class="n">st</span><span class="o">.</span><span class="n">integers</span><span class="p">(),</span> <span class="n">st</span><span class="o">.</span><span class="n">integers</span><span class="p">())</span>
<span class="k">def</span> <span class="nf">test_ints_are_commutative</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">):</span>
<span class="k">assert</span> <span class="n">x</span> <span class="o">+</span> <span class="n">y</span> <span class="o">==</span> <span class="n">y</span> <span class="o">+</span> <span class="n">x</span>
<span class="nd">@given</span><span class="p">(</span><span class="n">x</span><span class="o">=</span><span class="n">st</span><span class="o">.</span><span class="n">integers</span><span class="p">(),</span> <span class="n">y</span><span class="o">=</span><span class="n">st</span><span class="o">.</span><span class="n">integers</span><span class="p">())</span>
<span class="k">def</span> <span class="nf">test_ints_cancel</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">):</span>
<span class="k">assert</span> <span class="p">(</span><span class="n">x</span> <span class="o">+</span> <span class="n">y</span><span class="p">)</span> <span class="o">-</span> <span class="n">y</span> <span class="o">==</span> <span class="n">x</span>
<span class="nd">@given</span><span class="p">(</span><span class="n">st</span><span class="o">.</span><span class="n">lists</span><span class="p">(</span><span class="n">st</span><span class="o">.</span><span class="n">integers</span><span class="p">()))</span>
<span class="k">def</span> <span class="nf">test_reversing_twice_gives_same_list</span><span class="p">(</span><span class="n">xs</span><span class="p">):</span>
<span class="c1"># This will generate lists of arbitrary length (usually between 0 and</span>
<span class="c1"># 100 elements) whose elements are integers.</span>
<span class="n">ys</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">xs</span><span class="p">)</span>
<span class="n">ys</span><span class="o">.</span><span class="n">reverse</span><span class="p">()</span>
<span class="n">ys</span><span class="o">.</span><span class="n">reverse</span><span class="p">()</span>
<span class="k">assert</span> <span class="n">xs</span> <span class="o">==</span> <span class="n">ys</span>
<span class="nd">@given</span><span class="p">(</span><span class="n">st</span><span class="o">.</span><span class="n">tuples</span><span class="p">(</span><span class="n">st</span><span class="o">.</span><span class="n">booleans</span><span class="p">(),</span> <span class="n">st</span><span class="o">.</span><span class="n">text</span><span class="p">()))</span>
<span class="k">def</span> <span class="nf">test_look_tuples_work_too</span><span class="p">(</span><span class="n">t</span><span class="p">):</span>
<span class="c1"># A tuple is generated as the one you provided, with the corresponding</span>
<span class="c1"># types in those positions.</span>
<span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">t</span><span class="p">)</span> <span class="o">==</span> <span class="mi">2</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">],</span> <span class="nb">bool</span><span class="p">)</span>
<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">1</span><span class="p">],</span> <span class="nb">str</span><span class="p">)</span>
</pre></div>
</div>
<p>Note that as we saw in the above example you can pass arguments to <a class="reference internal" href="details.html#hypothesis.given" title="hypothesis.given"><code class="xref py py-func docutils literal"><span class="pre">@given</span></code></a>
either as positional or as keywords.</p>
</div>
<div class="section" id="where-to-start">
<h2>Where to start<a class="headerlink" href="#where-to-start" title="Permalink to this headline">¶</a></h2>
<p>You should now know enough of the basics to write some tests for your code
using Hypothesis. The best way to learn is by doing, so go have a try.</p>
<p>If you’re stuck for ideas for how to use this sort of test for your code, here
are some good starting points:</p>
<ol class="arabic simple">
<li>Try just calling functions with appropriate random data and see if they
crash. You may be surprised how often this works. e.g. note that the first
bug we found in the encoding example didn’t even get as far as our
assertion: It crashed because it couldn’t handle the data we gave it, not
because it did the wrong thing.</li>
<li>Look for duplication in your tests. Are there any cases where you’re testing
the same thing with multiple different examples? Can you generalise that to
a single test using Hypothesis?</li>
<li><a class="reference external" href="https://fsharpforfunandprofit.com/posts/property-based-testing-2/">This piece is designed for an F# implementation</a>, but
is still very good advice which you may find helps give you good ideas for
using Hypothesis.</li>
</ol>
<p>If you have any trouble getting started, don’t feel shy about
<a class="reference internal" href="community.html"><span class="doc">asking for help</span></a>.</p>
</div>
</div>
</div>
<div class="articleComments">
</div>
</div>
<footer>
<div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
<a href="details.html" class="btn btn-neutral float-right" title="Details and advanced features" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right"></span></a>
<a href="index.html" class="btn btn-neutral" title="Welcome to Hypothesis!" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left"></span> Previous</a>
</div>
<hr/>
<div role="contentinfo">
<p>
© Copyright 2013-2018, David R. MacIver.
</p>
</div>
Built with <a href="http://sphinx-doc.org/">Sphinx</a> using a <a href="https://github.com/snide/sphinx_rtd_theme">theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a>.
</footer>
</div>
</div>
</section>
</div>
<script type="text/javascript">
var DOCUMENTATION_OPTIONS = {
URL_ROOT:'./',
VERSION:'3.44.1',
COLLAPSE_INDEX:false,
FILE_SUFFIX:'.html',
HAS_SOURCE: true,
SOURCELINK_SUFFIX: '.txt'
};
</script>
<script type="text/javascript" src="_static/jquery.js"></script>
<script type="text/javascript" src="_static/underscore.js"></script>
<script type="text/javascript" src="_static/doctools.js"></script>
<script type="text/javascript" src="_static/js/theme.js"></script>
<script type="text/javascript">
jQuery(function () {
SphinxRtdTheme.StickyNav.enable();
});
</script>
</body>
</html>
|