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|
Feature: Any Instance
rspec-mocks provides two methods, `allow_any_instance_of` and
`expect_any_instance_of`, that will allow you to stub or mock any instance of a class. They
are used in place of [`allow`](../basics/allowing-messages) or [`expect`](../basics/expecting-messages):
```ruby
allow_any_instance_of(Widget).to receive(:name).and_return("Wibble")
expect_any_instance_of(Widget).to receive(:name).and_return("Wobble")
```
These methods add the appropriate stub or expectation to all instances of `Widget`.
You can also [configure the responses](../configuring-responses) in the same manner.
This feature is sometimes useful when working with legacy code, though in general we
discourage its use for a number of reasons:
* The `rspec-mocks` API is designed for individual object instances, but this feature
operates on entire classes of objects. As a result there are some semantically confusing
edge cases. For example, in `expect_any_instance_of(Widget).to
receive(:name).twice` it isn't clear whether a specific instance is expected to
receive `name` twice, or if two receives total are expected. (It's the former.)
* Using this feature is often a design smell. It may be that your test is trying to do too
much or that the object under test is too complex.
* It is the most complicated feature of `rspec-mocks`, and has historically received the
most bug reports. (None of the core team actively use it, which doesn't help.)
Scenario: Use `allow_any_instance_of` to stub a method
Given a file named "example_spec.rb" with:
"""ruby
RSpec.describe "allow_any_instance_of" do
it "returns the specified value on any instance of the class" do
allow_any_instance_of(Object).to receive(:foo).and_return(:return_value)
o = Object.new
expect(o.foo).to eq(:return_value)
end
end
"""
When I run `rspec example_spec.rb`
Then the examples should all pass
Scenario: Use `allow_any_instance_of` to stub multiple methods
Given a file named "example_spec.rb" with:
"""ruby
RSpec.describe "allow_any_instance_of" do
context "with receive_messages" do
it "stubs multiple methods" do
allow_any_instance_of(Object).to receive_messages(:foo => 'foo', :bar => 'bar')
o = Object.new
expect(o.foo).to eq('foo')
expect(o.bar).to eq('bar')
end
end
end
"""
When I run `rspec example_spec.rb`
Then the examples should all pass
Scenario: Stubbing any instance of a class with specific arguments
Given a file named "example_spec.rb" with:
"""ruby
RSpec.describe "allow_any_instance_of" do
context "with arguments" do
it "returns the stubbed value when arguments match" do
allow_any_instance_of(Object).to receive(:foo).with(:param_one, :param_two).and_return(:result_one)
allow_any_instance_of(Object).to receive(:foo).with(:param_three, :param_four).and_return(:result_two)
o = Object.new
expect(o.foo(:param_one, :param_two)).to eq(:result_one)
expect(o.foo(:param_three, :param_four)).to eq(:result_two)
end
end
end
"""
When I run `rspec example_spec.rb`
Then the examples should all pass
Scenario: Block implementation is passed the receiver as first arg
Given a file named "example_spec.rb" with:
"""ruby
RSpec.describe "allow_any_instance_of" do
it 'yields the receiver to the block implementation' do
allow_any_instance_of(String).to receive(:slice) do |value, start, length|
value[start, length]
end
expect('string'.slice(2, 3)).to eq('rin')
end
end
"""
When I run `rspec example_spec.rb`
Then the examples should all pass
Scenario: Use `expect_any_instance_of` to set a message expectation on any instance
Given a file named "example_spec.rb" with:
"""ruby
RSpec.describe "expect_any_instance_of" do
before do
expect_any_instance_of(Object).to receive(:foo)
end
it "passes when an instance receives the message" do
Object.new.foo
end
it "fails when no instance receives the message" do
Object.new.to_s
end
end
"""
When I run `rspec example_spec.rb`
Then it should fail with the following output:
| 2 examples, 1 failure |
| Exactly one instance should have received the following message(s) but didn't: foo |
|
