Improve error message when validating enum

lib/openapi_first/validation_format.rb

@@ -19,6 +19,11 @@ def self.error_details(error)
           title: "has not a valid #{error.dig('schema', 'format')} format",
           detail: "#{error['data'].inspect} is not a valid #{error.dig('schema', 'format')} format"
         }
+      elsif error['type'] == 'enum'
+        {
+          title: "value #{error['data'].inspect} is not defined in enum",
+          detail: "value can be one of #{error.dig('schema', 'enum')&.join(', ')}"
+        }
       elsif error['type'] == 'required'
         missing_keys = error['details']['missing_keys']
         {

spec/data/petstore-expanded.yaml

@@ -165,6 +165,9 @@ components:
       properties:
         type:
           type: string
+          enum:
+            - pet
+            - plant
         attributes:
           additionalProperties: false
           type: object

spec/request_validation/request_body_validation_spec.rb

@@ -29,7 +29,7 @@
 
     let(:request_body) do
       {
-        type: 'people',
+        type: 'pet',
         attributes: {
           name: 'Oscar'
         }
@@ -92,6 +92,18 @@
       expect(error[:source][:pointer]).to eq '/attributes'
     end
 
+    it 'returns 400 if value is not defined in enum' do
+      request_body[:type] = 'unknown-type'
+      header Rack::CONTENT_TYPE, 'application/json'
+      post path, json_dump(request_body)
+
+      expect(last_response.status).to be 400
+      error = response_body[:errors][0]
+      expect(error[:title]).to eq 'value "unknown-type" is not defined in enum'
+      expect(error[:source][:pointer]).to eq '/type'
+      expect(error[:detail]).to eq 'value can be one of pet, plant'
+    end
+
     it 'returns 400 if additional property is not allowed' do
       request_body[:attributes].update(foo: :bar)
       header Rack::CONTENT_TYPE, 'application/json'