Handle non-permitted params when comparing rules to request body

lib/typed_parameters/comparison.rb

@@ -1,9 +1,19 @@
 module TypedParameters
   class Comparison
+    # Example usage:
+    # Expected types for arguments indicated on the next line.
+    # Comparison.new(rules_format: RulesFormat, request_body: RequestBody)
+    #
     def initialize(rules_format:, request_body:)
       @rules_format, @request_body = rules_format, request_body
     end
 
+    # Example usage:
+    # comparison.errors =>
+    # Returns nil when there are no errors when comparing the
+    # rules_format to the request_body.
+    # Otherwise, returns an object where each key is the path to the
+    # problematic parameter and whose value describes the problem.
     def errors
       @errors = {}
 

spec/typed_parameters/comparison_spec.rb

@@ -25,10 +25,25 @@
       end
 
       context "when the request body does not adhere to the rules format" do
-        let(:name) { 1_000 }
+        context "when a non-specified parameter is included in the request body" do
+          let(:params) { { name: "M@", email: "[email protected]" } }
 
-        it "returns an object describing the invalid attribute" do
-          expect(subject).to eq({ "name" => "param_must_be_string" })
+          # NOTE: pick one of the following 2 test cases as desired behavior
+          it "ignores the non-whitelisted param" do
+            expect(subject).to eq nil
+          end
+
+          it "adds an error for the non-whitelisted param" do
+            expect(subject).to eq({ "email" => "non_permitted_param" })
+          end
+        end
+
+        context "when the require parameter is of the wrong type" do
+          let(:name) { 1_000 }
+
+          it "returns an object describing the invalid attribute" do
+            expect(subject).to eq({ "name" => "param_must_be_string" })
+          end
         end
       end
     end