Consolidate set_session and set_flash APIs

* Refactor so they both use SetSessionOrFlashMatcher internally
* Remove `set_session['key']` in favor of `set_session('key')`
* `set_flash['key'].to(nil)` no longer works if set_flash has never been
  set

spec/support/unit/shared_examples/set_session_or_flash.rb

@@ -0,0 +1,355 @@
+shared_examples_for 'set session or flash matcher' do
+  context 'without any qualifiers' do
+    it 'produces the right description' do
+      expected_description = "should set any key in #{store_name}"
+      matcher = set_store
+
+      expect(matcher.description).to eq expected_description
+    end
+
+    context 'in the positive' do
+      context 'if the store is not empty' do
+        it 'accepts' do
+          controller = controller_with_store('any key' => 'any value')
+          expect(controller).to set_store
+        end
+      end
+
+      context 'if the store is empty' do
+        it 'rejects' do
+          controller = controller_with_empty_store
+          expect(controller).not_to set_store
+        end
+
+        it 'produces the correct failure message' do
+          controller = controller_with_empty_store
+          expected_message = %<Expected #{controller.class} to set any key in #{store_name}, but it did not>
+
+          expect { expect(controller).to set_store }.
+            to fail_with_message(expected_message)
+        end
+      end
+    end
+
+    context 'in the negative' do
+      context 'if the given key is present in the store' do
+        it 'produces the correct failure message' do
+          controller = controller_with_store('any key' => 'any value')
+          expected_message = %<Expected #{controller.class} not to set any key in #{store_name}, but it did>
+          assertion = proc do
+            expect(controller).not_to set_store
+          end
+
+          expect(&assertion).to fail_with_message(expected_message)
+        end
+      end
+    end
+  end
+
+  context 'with #[]' do
+    it 'produces the right description' do
+      matcher = set_store['the key']
+      expected_description = %<should set #{store_name}["the key"]>
+
+      expect(matcher.description).to eq expected_description
+    end
+
+    context 'in the positive' do
+      context 'if the given key is present in the store' do
+        it 'accepts' do
+          controller = controller_with_store('the key' => 'any value')
+          expect(controller).to set_store['the key']
+        end
+      end
+
+      context 'if the given key is not present in the store' do
+        it 'rejects' do
+          controller = controller_with_empty_store
+          expect(controller).not_to set_store['the key']
+        end
+
+        it 'produces the correct failure message' do
+          controller = controller_with_empty_store
+          expected_message = %<Expected #{controller.class} to set #{store_name}["the key"], but it did not>
+          assertion = proc do
+            expect(controller).to set_store['the key']
+          end
+
+          expect(&assertion).to fail_with_message(expected_message)
+        end
+      end
+    end
+
+    context 'in the negative' do
+      context 'if the given key is present in the store' do
+        it 'produces the correct failure message' do
+          controller = controller_with_store('the key' => 'any value')
+          expected_message = %<Expected #{controller.class} not to set #{store_name}["the key"], but it did>
+          assertion = proc do
+            expect(controller).not_to set_store['the key']
+          end
+
+          expect(&assertion).to fail_with_message(expected_message)
+        end
+      end
+    end
+  end
+
+  context 'with #to' do
+    context 'given a static value' do
+      it 'produces the right description' do
+        matcher = set_store.to('the value')
+        expected_description = %<should set any key in #{store_name} to "the value">
+
+        expect(matcher.description).to eq expected_description
+      end
+
+      context 'in the positive' do
+        context 'if the given value is present in the store' do
+          it 'accepts' do
+            controller = controller_with_store('any key' => 'the value')
+            expect(controller).to set_store.to('the value')
+          end
+
+          it 'accepts given a value of nil' do
+            controller = controller_with_store('any key' => nil)
+            expect(controller).to set_store.to(nil)
+          end
+
+          it 'accepts given a value of false' do
+            controller = controller_with_store('any key' => false)
+            expect(controller).to set_store.to(false)
+          end
+        end
+
+        context 'if the given value is not present in the store' do
+          it 'rejects' do
+            controller = controller_with_empty_store
+            expect(controller).not_to set_store.to('the value')
+          end
+
+          it 'rejects checking for nil' do
+            controller = controller_with_empty_store
+            expect(controller).not_to set_store.to(nil)
+          end
+
+          it 'produces the correct failure message' do
+            controller = controller_with_empty_store
+            expected_message = %<Expected #{controller.class} to set any key in #{store_name} to "the value", but it did not>
+            assertion = proc do
+              expect(controller).to set_store.to('the value')
+            end
+
+            expect(&assertion).to fail_with_message(expected_message)
+          end
+        end
+      end
+
+      context 'in the negative' do
+        context 'if the given value is present in the store' do
+          it 'produces the correct failure message' do
+            controller = controller_with_store('any key' => 'the value')
+            expected_message = %<Expected #{controller.class} not to set any key in #{store_name} to "the value", but it did>
+            assertion = proc do
+              expect(controller).not_to set_store.to('the value')
+            end
+
+            expect(&assertion).to fail_with_message(expected_message)
+          end
+        end
+      end
+    end
+
+    context 'given a regexp' do
+      it 'produces the right description' do
+        matcher = set_store.to(/value/)
+        expected_description = %<should set any key in #{store_name} to a value matching /value/>
+
+        expect(matcher.description).to eq expected_description
+      end
+
+      context 'in the positive' do
+        context 'if the given value is present in the store' do
+          it 'accepts' do
+            controller = controller_with_store('any key' => 'the value')
+            expect(controller).to set_store.to(/value/)
+          end
+
+          it 'accepts given a value of nil' do
+            controller = controller_with_store('any key' => nil)
+            expect(controller).to set_store.to(nil)
+          end
+
+          it 'accepts given a value of false' do
+            controller = controller_with_store('any key' => false)
+            expect(controller).to set_store.to(false)
+          end
+        end
+
+        context 'if the given value is not present in the store' do
+          it 'rejects' do
+            controller = controller_with_empty_store
+            expect(controller).not_to set_store.to(/value/)
+          end
+
+          it 'produces the correct failure message' do
+            controller = controller_with_empty_store
+            expected_message = %<Expected #{controller.class} to set any key in #{store_name} to a value matching /value/, but it did not>
+            assertion = proc do
+              expect(controller).to set_store.to(/value/)
+            end
+
+            expect(&assertion).to fail_with_message(expected_message)
+          end
+        end
+      end
+
+      context 'in the negative' do
+        context 'if the given value is present in the store' do
+          it 'produces the correct failure message' do
+            controller = controller_with_store('any key' => 'the value')
+            expected_message = %<Expected #{controller.class} not to set any key in #{store_name} to a value matching /value/, but it did>
+            assertion = proc do
+              expect(controller).not_to set_store.to(/value/)
+            end
+
+            expect(&assertion).to fail_with_message(expected_message)
+          end
+        end
+      end
+    end
+  end
+
+  context 'with #[] + #to' do
+    context 'given a static value' do
+      it 'produces the right description' do
+        expected_description = %<should set #{store_name}["the key"] to "the value">
+        matcher = set_store['the key'].to('the value')
+
+        expect(matcher.description).to eq expected_description
+      end
+
+      context 'in the positive' do
+        context 'if the given value is present in the store' do
+          it 'accepts' do
+            controller = controller_with_store('the key' => 'the value')
+            expect(controller).to set_store['the key'].to('the value')
+          end
+        end
+
+        context 'if the given value is not present in the store' do
+          it 'rejects' do
+            controller = controller_with_empty_store
+            expect(controller).not_to set_store['the key'].to('the value')
+          end
+
+          it 'produces the correct failure message' do
+            controller = controller_with_empty_store
+            expected_message = %<Expected #{controller.class} to set #{store_name}["the key"] to "the value", but it did not>
+            assertion = proc do
+              expect(controller).to set_store['the key'].to('the value')
+            end
+
+            expect(&assertion).to fail_with_message(expected_message)
+          end
+        end
+      end
+
+      context 'in the negative' do
+        context 'if the given value is present in the store' do
+          it 'produces the correct failure message' do
+            controller = controller_with_store('the key' => 'the value')
+            expected_message = %<Expected #{controller.class} not to set #{store_name}["the key"] to "the value", but it did>
+            assertion = proc do
+              expect(controller).not_to set_store['the key'].to('the value')
+            end
+
+            expect(&assertion).to fail_with_message(expected_message)
+          end
+        end
+      end
+    end
+
+    context 'given a dynamic value' do
+      it 'produces the right description' do
+        context = double('context', method_in_context: 'the value')
+        matcher = set_store['the key'].
+          in_context(context).
+          to { method_in_context }
+        expected_description = %<should set #{store_name}["the key"] to "the value">
+
+        expect(matcher.description).to eq expected_description
+      end
+
+      context 'in the positive' do
+        context 'if the value evaluated in the context is present in the store' do
+          it 'accepts' do
+            controller = controller_with_store('the key' => 'the value')
+            context = double('context', method_in_context: 'the value')
+
+            expect(controller).to set_store['the key'].
+              in_context(context).
+              to { method_in_context }
+          end
+        end
+
+        context 'if the value evaluated in the context is not present in the store' do
+          it 'rejects' do
+            controller = controller_with_empty_store
+            context = double('context', method_in_context: 'the value')
+
+            expect(controller).not_to set_store['the key'].
+              in_context(context).
+              to { method_in_context }
+          end
+
+          it 'produces the correct failure message' do
+            controller = controller_with_empty_store
+            context = double('context', method_in_context: 'the value')
+            expected_message = %<Expected #{controller.class} to set #{store_name}["the key"] to "the value", but it did not>
+            assertion = proc do
+              expect(controller).to set_store['the key'].
+                in_context(context).
+                to { method_in_context }
+            end
+
+            expect(&assertion).to fail_with_message(expected_message)
+          end
+        end
+      end
+
+      context 'in the negative' do
+        context 'if the value evaluated in the context is present in the store' do
+          it 'produces the correct failure message' do
+            context = double('context', method_in_context: 'the value')
+            controller = controller_with_store('the key' => 'the value')
+            expected_message = %<Expected #{controller.class} not to set #{store_name}["the key"] to "the value", but it did>
+            assertion = proc do
+              expect(controller).not_to set_store['the key'].
+                in_context(context).
+                to { method_in_context }
+            end
+
+            expect(&assertion).to fail_with_message(expected_message)
+          end
+        end
+      end
+    end
+  end
+
+  def controller_with_empty_store
+    build_fake_response
+  end
+
+  def controller_with_store(store_contents)
+    context = self
+
+    build_fake_response do
+      store = context.store_within(self)
+
+      store_contents.each do |key, value|
+        store[key] = value
+      end
+    end
+  end
+end