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Feature: shared examples
Shared examples let you describe behaviour of classes or modules. When declared,
a shared group's content is stored. It is only realized in the context of
another example group, which provides any context the shared group needs to
run.
A shared group is included in another group using any of:
```ruby
include_examples "name" # include the examples in the current context
it_behaves_like "name" # include the examples in a nested context
it_should_behave_like "name" # include the examples in a nested context
matching metadata # include the examples in the current context
```
**WARNING:** Files containing shared groups must be loaded before the files that
use them. While there are conventions to handle this, RSpec does _not_ do
anything special (like autoload). Doing so would require a strict naming
convention for files that would break existing suites.
**WARNING:** When you include parameterized examples in the current context multiple
times, you may override previous method definitions and last declaration wins.
So if you have this kind of shared example (or shared context)
```ruby
RSpec.shared_examples "some example" do |parameter|
\# Same behavior is triggered also with either `def something; 'some value'; end`
\# or `define_method(:something) { 'some value' }`
let(:something) { parameter }
it "uses the given parameter" do
expect(something).to eq(parameter)
end
end
RSpec.describe SomeClass do
include_examples "some example", "parameter1"
include_examples "some example", "parameter2"
end
```
You're actually doing this (notice that first example will fail):
```ruby
RSpec.describe SomeClass do
\# Reordered code for better understanding of what is happening
let(:something) { "parameter1" }
let(:something) { "parameter2" }
it "uses the given parameter" do
\# This example will fail because last let "wins"
expect(something).to eq("parameter1")
end
it "uses the given parameter" do
expect(something).to eq("parameter2")
end
end
```
To prevent this kind of subtle error a warning is emitted if you declare multiple
methods with the same name in the same context. Should you get this warning
the simplest solution is to replace `include_examples` with `it_behaves_like`, in this
way method overriding is avoided because of the nested context created by `it_behaves_like`
Conventions:
------------
1. The simplest approach is to require files with shared examples explicitly
from the files that use them. Keep in mind that RSpec adds the `spec`
directory to the `LOAD_PATH`, so you can say `require
'shared_examples_for_widgets'` to require a file at
`#{PROJECT_ROOT}/spec/shared_examples_for_widgets.rb`.
2. One convention is to put files containing shared examples in `spec/support/`
and require files in that directory from `spec/spec_helper.rb`:
```ruby
Dir["./spec/support/**/*.rb"].sort.each { |f| require f }
```
Historically, this was included in the generated `spec/spec_helper.rb` file in
`rspec-rails`. However, in order to keep your test suite boot time down,
it's a good idea to not autorequire all files in a directory like this.
When running only one spec file, loading unneeded dependencies or performing
unneeded setup can have a significant, noticable effect on how long it takes
before the first example runs.
3. When all of the groups that include the shared group reside in the same file,
just declare the shared group in that file.
Scenario: Shared examples group included in two groups in one file
Given a file named "collection_spec.rb" with:
"""ruby
require "set"
RSpec.shared_examples "a collection" do
let(:collection) { described_class.new([7, 2, 4]) }
context "initialized with 3 items" do
it "says it has three items" do
expect(collection.size).to eq(3)
end
end
describe "#include?" do
context "with an item that is in the collection" do
it "returns true" do
expect(collection.include?(7)).to be_truthy
end
end
context "with an item that is not in the collection" do
it "returns false" do
expect(collection.include?(9)).to be_falsey
end
end
end
end
RSpec.describe Array do
it_behaves_like "a collection"
end
RSpec.describe Set do
it_behaves_like "a collection"
end
"""
When I run `rspec collection_spec.rb --format documentation`
Then the examples should all pass
And the output should contain:
"""
Array
behaves like a collection
initialized with 3 items
says it has three items
#include?
with an item that is in the collection
returns true
with an item that is not in the collection
returns false
Set
behaves like a collection
initialized with 3 items
says it has three items
#include?
with an item that is in the collection
returns true
with an item that is not in the collection
returns false
"""
Scenario: Providing context to a shared group using a block
Given a file named "shared_example_group_spec.rb" with:
"""ruby
require "set"
RSpec.shared_examples "a collection object" do
describe "<<" do
it "adds objects to the end of the collection" do
collection << 1
collection << 2
expect(collection.to_a).to match_array([1, 2])
end
end
end
RSpec.describe Array do
it_behaves_like "a collection object" do
let(:collection) { Array.new }
end
end
RSpec.describe Set do
it_behaves_like "a collection object" do
let(:collection) { Set.new }
end
end
"""
When I run `rspec shared_example_group_spec.rb --format documentation`
Then the examples should all pass
And the output should contain:
"""
Array
behaves like a collection object
<<
adds objects to the end of the collection
Set
behaves like a collection object
<<
adds objects to the end of the collection
"""
Scenario: Passing parameters to a shared example group
Given a file named "shared_example_group_params_spec.rb" with:
"""ruby
RSpec.shared_examples "a measurable object" do |measurement, measurement_methods|
measurement_methods.each do |measurement_method|
it "should return #{measurement} from ##{measurement_method}" do
expect(subject.send(measurement_method)).to eq(measurement)
end
end
end
RSpec.describe Array, "with 3 items" do
subject { [1, 2, 3] }
it_should_behave_like "a measurable object", 3, [:size, :length]
end
RSpec.describe String, "of 6 characters" do
subject { "FooBar" }
it_should_behave_like "a measurable object", 6, [:size, :length]
end
"""
When I run `rspec shared_example_group_params_spec.rb --format documentation`
Then the examples should all pass
And the output should contain:
"""
Array with 3 items
it should behave like a measurable object
should return 3 from #size
should return 3 from #length
String of 6 characters
it should behave like a measurable object
should return 6 from #size
should return 6 from #length
"""
Scenario: Aliasing `it_should_behave_like` to `it_has_behavior`
Given a file named "shared_example_group_spec.rb" with:
"""ruby
RSpec.configure do |c|
c.alias_it_should_behave_like_to :it_has_behavior, 'has behavior:'
end
RSpec.shared_examples 'sortability' do
it 'responds to <=>' do
expect(sortable).to respond_to(:<=>)
end
end
RSpec.describe String do
it_has_behavior 'sortability' do
let(:sortable) { 'sample string' }
end
end
"""
When I run `rspec shared_example_group_spec.rb --format documentation`
Then the examples should all pass
And the output should contain:
"""
String
has behavior: sortability
responds to <=>
"""
Scenario: Sharing metadata automatically includes shared example groups
Given a file named "shared_example_metadata_spec.rb" with:
"""ruby
RSpec.shared_examples "shared stuff", :a => :b do
it 'runs wherever the metadata is shared' do
end
end
RSpec.describe String, :a => :b do
end
"""
When I run `rspec shared_example_metadata_spec.rb`
Then the output should contain:
"""
1 example, 0 failures
"""
Scenario: Shared examples are nestable by context
Given a file named "context_specific_examples_spec.rb" with:
"""Ruby
RSpec.describe "shared examples" do
context "per context" do
shared_examples "shared examples are nestable" do
specify { expect(true).to eq true }
end
it_behaves_like "shared examples are nestable"
end
end
"""
When I run `rspec context_specific_examples_spec.rb`
Then the output should contain:
"""
1 example, 0 failures
"""
Scenario: Shared examples are accessible from offspring contexts
Given a file named "context_specific_examples_spec.rb" with:
"""Ruby
RSpec.describe "shared examples" do
shared_examples "shared examples are nestable" do
specify { expect(true).to eq true }
end
context "per context" do
it_behaves_like "shared examples are nestable"
end
end
"""
When I run `rspec context_specific_examples_spec.rb`
Then the output should contain:
"""
1 example, 0 failures
"""
And the output should not contain:
"""
Accessing shared_examples defined across contexts is deprecated
"""
Scenario: Shared examples are isolated per context
Given a file named "isolated_shared_examples_spec.rb" with:
"""Ruby
RSpec.describe "shared examples" do
context do
shared_examples "shared examples are isolated" do
specify { expect(true).to eq true }
end
end
context do
it_behaves_like "shared examples are isolated"
end
end
"""
When I run `rspec isolated_shared_examples_spec.rb`
Then the output should contain:
"""
Could not find shared examples \"shared examples are isolated\"
"""