Add a warning when doc string is not a string

#2921 (comment)

Author: pirj

lib/rspec/core/example_group.rb

@@ -146,6 +146,10 @@ def self.define_example_method(name, extra_options={})
         idempotently_define_singleton_method(name) do |*all_args, &block|
           desc, *args = *all_args
 
+          unless NilClass === desc || String === desc
+            RSpec.warning "`#{desc.inspect}` is used as example doc string. Use a string instead"
+          end
+
           options = Metadata.build_hash_from(args)
           options.update(:skip => RSpec::Core::Pending::NOT_YET_IMPLEMENTED) unless block
           options.update(extra_options)
@@ -264,6 +268,11 @@ def self.define_example_group_method(name, metadata={})
 
           begin
             description = args.shift
+
+            unless NilClass === description || String === description || Module === description
+              RSpec.warning "`#{description.inspect}` is used as example group doc string. Use a string instead"
+            end
+
             combined_metadata = metadata.dup
             combined_metadata.merge!(args.pop) if args.last.is_a? Hash
             args << combined_metadata

spec/rspec/core/example_group_spec.rb

@@ -1231,6 +1231,72 @@ def extract_execution_results(group)
 
     end
 
+    describe "example group doc string" do
+      it "accepts a string for an example group doc string" do
+        expect { RSpec.describe 'MyClass' }.not_to output.to_stderr
+      end
+
+      it "accepts a class for an example group doc string" do
+        expect { RSpec.describe Numeric }.not_to output.to_stderr
+      end
+
+      it "accepts a module for an example group doc string" do
+        expect { RSpec.describe RSpec }.not_to output.to_stderr
+      end
+
+      it "accepts example group without a doc string" do
+        expect { RSpec.describe }.not_to output.to_stderr
+      end
+
+      it "emits a warning when a Symbol is used as an example group doc string" do
+        expect { RSpec.describe :foo }
+          .to output(/`:foo` is used as example group doc string. Use a string instead/)
+          .to_stderr
+      end
+
+      it "emits a warning when a Hash is used as an example group doc string" do
+        expect { RSpec.describe(foo: :bar) { } }
+          .to output(/`{:foo=>:bar}` is used as example group doc string. Use a string instead/)
+          .to_stderr
+      end
+    end
+
+    describe "example doc string" do
+      let(:group) { RSpec.describe }
+
+      it "accepts a string for an example doc string" do
+        expect { group.it('MyClass') { } }.not_to output.to_stderr
+      end
+
+      it "accepts example without a doc string" do
+        expect { group.it { } }.not_to output.to_stderr
+      end
+
+      it "emits a warning when a Class is used as an example doc string" do
+        expect { group.it(Numeric) { } }
+          .to output(/`Numeric` is used as example doc string. Use a string instead/)
+          .to_stderr
+      end
+
+      it "emits a warning when a Module is used as an example doc string" do
+        expect { group.it(RSpec) { } }
+          .to output(/`RSpec` is used as example doc string. Use a string instead/)
+          .to_stderr
+      end
+
+      it "emits a warning when a Symbol is used as an example doc string" do
+        expect { group.it(:foo) { } }
+          .to output(/`:foo` is used as example doc string. Use a string instead/)
+          .to_stderr
+      end
+
+      it "emits a warning when a Hash is used as an example doc string" do
+        expect { group.it(foo: :bar) { } }
+          .to output(/`{:foo=>:bar}` is used as example doc string. Use a string instead/)
+          .to_stderr
+      end
+    end
+
     describe Object, "describing nested example_groups", :little_less_nested => 'yep' do
 
       describe "A sample nested group", :nested_describe => "yep" do