Running Rspec examples by name, or: Running a single shared example

When an Rspec example fails, I usually investigate by running that example again using rspec <file:line>. However, this does not work with shared examples, since Rspec doesn't know in which context the shared example should be run.

But there is a different way: You can run the shared example using the -e, --example option. It takes a string value and runs all scenarios containing that substring in their full description.

This allows you to run a single uniquely named example, all examples with
similar names, all the examples in a uniquely named group, etc, etc.

You can also use the option more than once to specify multiple example
matches.

Example

Let the following setup:

# my_model_spec.rb
describe MyModel do
  it 'perfoms a test'
  it_behaves_like 'something shared'
end

# something_shared.rb
shared_examples_for 'something shared' do
  it 'does something'
end

When the shared example "it does something" fails, you can run it like this:

rspec spec/models/my_model_spec.rb --example 'something'

If you are using Rspec >= 3.3 you could also run a shared example by it's ID.

The ID of an Example/-Group is the combination of the filename and the nested index (starting from 1) in brackets. To run the shared example from above you could execute:

rspec spec/models/my_model_spec.rb[1:2:1]

Note that if an example from a shared example group fails, RSpec will print out the file name with that ID. You just need to paste it to your console.

Further Explanation regarding the IDs of Example/-Groups Show archive.org snapshot :
The ID of the ExampleGroup created by describe MyModel is spec/models/my_model_spec.rb[1].
The ID of the ExampleGroup created by it 'performs a test' is spec/models/my_model_spec.rb[1:1].
The ID of the ExampleGroup created by it_behaves_like 'something shared' is spec/models/my_model_spec.rb[1:2] as it is the second ExampleGroup in the MyModel-ExampleGroup.
Then rpsec spec/models/my_model_spec.rb[1:2:1] is the first example (it 'does something') of this group.