WRITING CUSTOM RSPEC MATCHERS

Note that we can change the block argument names to match our domain. Test code is code like any other code, which needs to be maintained. Extending our custom matcher further Our custom matcher does the job but there are some potential problems with it. Note that we can change the block argument names to match our domain. RSpec dumps the actual and expected values and combines them with the name of our matcher to create a generic error message. We define our own domain-specific assertions and use them to compose readable specifications. This is the place where we implement our custom logic:.

This is the place where we implement our custom logic:. However, the APIs can differ e. XML str end end. We can improve our matcher further with a custom exception message. We can introduce a helper method to make things pretty again:.

I believe you should start writing custom matchers as soon as possible in a project. We can therefore create a new file. It all boils down to coming up with a true or false response to indicate whether the test passed or failed. This example uses RSpec 3.

writing custom rspec matchers

It is probably a good idea to tighten up that if statement with an elsif for Rack:: Matchers can be written as plain old Ruby objects, as long as they conform to a specific API — methods named like the blocks in our previous example. It matcherx needs to be well-factored and use rwpec domain language. This is the place where we implement our custom logic:.

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We want to assert that sensitive information is omitted from the XML for unauthorised users. We define our own domain-specific assertions, and use them to compose readable specifications. Matchers can be written as plain old Ruby objects, as long as they conform to a specific API — methods named like the blocks in our previous example.

Writing Custom RSpec Matchers

Custom RSpec matchers can help with this problem. This helps you build a suite of easily re-usable matchers that the entire team can use. RSpec will, by default, load all Ruby files under.

This customm demonstrate the difference between a generic, re-usable matcher to hide implementation details from the reader of the code, and modelling your domain language so you can write human-friendly specifications.

ArgumentError – occures, but there might be edge matcgers where you want to pass the exception to the user. Accepting a string in our match block — rather than a response object — helps keep our matcher generic enough that we can re-use it later.

How to Use Custom RSpec Matchers to Specify Behaviour

Take care to handle exceptions appropriately in your matcher, e. Defining custom RSpec matchers is really easy and a great way to increase the readability of your tests.

More about adding a collaborator. Test code needs to be both run by computers and read by humans.

Browse documentation Keyword search. Note that we can change the block argument names to match our domain.

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writing custom rspec matchers

Soon you’ll be able to also add collaborators here! Do not handle them all in one.

You might rsprc that this matcher is not quite high-level enough to actually model our domain. We can improve our matcher further with a custom exception message. You should handle each StandardError with care!

writing custom rspec matchers

These are often useful for expressing expectations in the domain of your application. You can find more information on defining fluent, chained matchers, diffable matchers and accepting blocks as arguments in the RSpec documentation. So, class-based matchers usually come with helper methods to marchers specifications readable and hide implementation details from the reader.

This is admittedly more code, and arguably less obvious than the DSL-version — but it is easier to refactor.

Writing custom RSpec matchers by Arjan van der Gaag

Learn more and download a free copy. May your tests now be more readable…. This gave us the opportunity to use the much terser ternary operator and split out the fetching of the status code from the matcher comparison.

We could write the above matcher as a class as writihg.