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    <p>It's complicated. Race conditions are so nasty precisely because they are so difficult to reproduce. Internally, <code>save</code> goes something like this:</p> <ol> <li>Validate.</li> <li>Write to database.</li> </ol> <p>So, to reproduce the timing problem, you'd need to arrange the two <code>save</code> calls to overlap like this (pseudo-Rails):</p> <pre><code>a.validate # first half of a.save b.validate # first half of b.save a.write_to_db # second half of a.save b.write_to_db # second half of b.save </code></pre> <p>but you can't open up the <code>save</code> method and fiddle with its internals quite so easily.</p> <p>But (and this is a big but), <a href="http://guides.rubyonrails.org/active_record_validations_callbacks.html#skipping-validations" rel="nofollow">you can skip the validations entirely</a>:</p> <blockquote> <p>Note that <code>save</code> also has the ability to skip validations if passed <code>:validate =&gt; false</code> as argument. This technique should be used with caution.</p> </blockquote> <p>So if you use</p> <pre><code>b.save(:validate =&gt; false) </code></pre> <p>you should get just the "write to database" half of <code>b</code>'s <code>save</code> and send your data to the database without validation. That should trigger a constraint violation in the database and I'm pretty sure that will raise an <a href="http://api.rubyonrails.org/classes/ActiveRecord/StatementInvalid.html" rel="nofollow">ActiveRecord::StatementInvalid</a> exception so I think you'll need to look for an exception rather than just a false return from <code>save</code>:</p> <pre><code>b.save(:validate =&gt; false).should raise_exception(ActiveRecord::StatementInvalid) </code></pre> <p>You can tighten that up to look for the specific exception message as well. I don't have anything handy to test this test with so try it out in the Rails console and adjust your spec appropriately.</p>
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    1. COLovely. Thanks. It took me several tries to check because... I had actually done the uniqueness wrong, and my indices were **not**, in fact, unique. The actual error from the console was `ActiveRecord::RecordNotUnique: SQLite3::SQLException: column email is not unique: ...`. And, ultimately, I needed `lambda` to check the exception thing: `lambda { B.save(:validate => false ) }.should raise_exception(ActiveRecord::RecordNotUnique)`
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    2. CO@mcdave: Cool, tests are supposed to find bugs :)
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