[expectations] Add chained matchers example to raise_error (rspec/rsp…

…ec-expectations#1087)

* Add chained matchers example to raise_error

Being new to rspec, it wasn't clear that I could pass composed matchers to 'raise_error'.  This commit adds an example of a chained matcher being passed to 'raise_error'. This is useful for testing custom attributes on an error while still satisfying the one 'expect' statement per test case enforced by rubocop-rspec. 

See rubocop/rubocop-rspec#379 for more details.

---
This commit was imported from rspec/rspec-expectations@dc0ecfd.

rspec-expectations/features/built_in_matchers/raise_error.feature

@@ -26,6 +26,7 @@ Feature: `raise_error` matcher
     expect { raise "oops" }.to raise_error(/op/)
     expect { raise "oops" }.to raise_error(RuntimeError, "oops")
     expect { raise "oops" }.to raise_error(RuntimeError, /op/)
+    expect { raise "oops" }.to raise_error(an_instance_of(RuntimeError).and having_attributes(message: "oops"))
     ```
 
   Scenario: expect any error
@@ -131,6 +132,19 @@ Feature: `raise_error` matcher
       When I run `rspec example_spec`
       Then the example should pass
 
+  Scenario: set expectations on error object with chained matchers
+    Given a file named "example_spec" with:
+      """
+      RSpec.describe "composing matchers" do
+        it "raises StandardError" do
+          expect { raise StandardError, "my message" }.
+            to raise_error(an_instance_of(StandardError).and having_attributes({"message" => "my message"}))
+        end
+      end
+      """
+      When I run `rspec example_spec`
+      Then the example should pass
+
   Scenario: expect no error at all
     Given a file named "example_spec" with:
       """