OmbuLabs Blog

The Lean Software Boutique

Articles about Rspec

'Flaky' tests: a short story

One of the hardest failing tests to debug are those which fail randomly, also known as "flaky" tests. You write your test cases, you run the tests in your environment (in random order), and see them all pass. Afterwards, you push your code, your CI server runs them and one test fails.

This is not an uncommon scenario, and one too common when using integration tests which use JS, with Capybara-Webkit or Selenium. But if your failing test doesn't communicate with an external API, doesn't use JS, and passes locally, it can be a bit nerve-wracking.

After you have identified the failing test, and it still passes after running it locally, one way to figure out why it's failing is running its context multiple times.

To automate this process a bit, I like to use the following command:

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Brief look at RSpec's formatting options

A few weeks ago, I noticed weird output in the RSpec test suite (~4000 tests) for a Rails application:

.............................................................................................unknown OID 353414: failed to recognize type of '<field>'. It will be treated as String  ...........................................................................................................................................

This Rails app uses a PostgreSQL database. After some Googling, it turns out that this is a warning from PostgreSQL. When the database doesn't recognize the type to use for a column, it casts to string by default.

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Spy vs Double vs Instance Double

When writing tests for services, you may sometimes want to use mock objects instead of real objects. In case you're using ActiveRecord and real objects, your tests may hit the database and slow down your suite. The latest release of the rspec-mocks library bundled with RSpec 3 includes at least three different ways to implement a mock object.

Let's discuss some of the differences between a spy, a double and an instance_double. First, the spy:

[1] pry(main)> require 'rspec/mocks/standalone'
=> true
[2] pry(main)> user_spy = spy(User)
=> #<Double User>
[3] pry(main)> spy.whatever_method
=> #<Double (anonymous)>
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