Add better error handling to .find

* Offers better ActiveRecord-like errors when trying to call .find with
  either no params, or an empty params hash

* Raises an explicit ResourceNotFound error when a 404 is returned,
  regardless of whether or not the response was parseable.

lib/frenetic/concerns/member_rest_methods.rb

@@ -6,9 +6,15 @@ module MemberRestMethods
 
     module ClassMethods
       def find(params)
+        fail ResourceNotFound.new(self, params) if params.blank?
         params = { id:params } unless params.is_a?(Hash)
         return as_mock(params) if test_mode?
-        response = api.get(member_url(params))
+        begin
+          response = api.get(member_url(params))
+        rescue ClientParsingError, ClientError => ex
+          raise if ex.status != 404
+          raise ResourceNotFound.new(self, params)
+        end
         new(response.body) if response.success?
       end
 

lib/frenetic/errors.rb

@@ -127,12 +127,14 @@ class ResponseError < Error
     attr_reader :env, :error, :method, :status, :url
     def initialize(env)
       env ||= {}
-      body = env.fetch(:body, {})
-      @env = env
-      @error = body['error']
-      @method = env[:method]
-      @status = env[:status]
-      @url = env[:url]
+      if env.respond_to?(:fetch)
+        body = env.fetch(:body, {})
+        @env = env
+        @error = body['error']
+        @method = env[:method]
+        @status = env[:status]
+        @url = env[:url]
+      end
       super(message)
     end
 
@@ -144,6 +146,34 @@ def message
   # Raised when a network response returns a 400-level error
   ClientError = Class.new(ResponseError)
 
+  # Raise when a network reponse returns a 404 Not Found error
+  class ResourceNotFound < ClientError
+    def initialize(resource, params)
+      @resource = resource.to_s.demodulize
+      @params = params
+      @status = 404
+      super(message)
+    end
+
+    def message
+      if @params.blank?
+        "Couldn't find #{@resource} without an ID"
+      else
+        "Couldn't find #{@resource} with #{stringified_params}"
+      end
+    end
+
+  private
+
+    def stringified_params
+      @params.each_with_object([]) do |*pairs, agg|
+        agg.concat(pairs)
+      end.map do |pair|
+        pair.join('=')
+      end.join(', ')
+    end
+  end
+
   # Raised when a network response returns a 500-level error
   ServerError = Class.new(ResponseError)
 

spec/concerns/member_rest_methods_spec.rb

@@ -17,9 +17,11 @@
   end
 
   describe '.find' do
+    let(:params) { 1 }
+
     before { @stubs.api_description }
 
-    subject { MyTempResource.find 1 }
+    subject { MyTempResource.find(params) }
 
     context 'for a known instance' do
       before { @stubs.known_instance }
@@ -41,7 +43,23 @@
       before { @stubs.unknown_instance }
 
       it 'raises an error' do
-        expect{subject}.to raise_error Frenetic::ClientError
+        expect{subject}.to raise_error Frenetic::ResourceNotFound, %q(Couldn't find MyTempResource with id=1)
+      end
+
+      context 'with an unparseable response' do
+        before { @stubs.invalid_unknown_instance }
+
+        it 'raises an error' do
+          expect{subject}.to raise_error Frenetic::ResourceNotFound, %q(Couldn't find MyTempResource with id=1)
+        end
+      end
+    end
+
+    context 'that results in a client-level error' do
+      before { @stubs.api_client_error }
+
+      it 'raises an error' do
+        expect{subject}.to raise_error Frenetic::ClientError, %q(422 Unprocessable Entity)
       end
     end
 
@@ -56,6 +74,14 @@
       it 'returns a mock resource' do
         expect(subject).to be_an_instance_of MyMockResource
       end
+
+      context 'with blank parameters' do
+        let(:params) { {} }
+
+        it 'raises an error' do
+          expect{subject}.to raise_error Frenetic::ResourceNotFound, %q(Couldn't find MyTempResource without an ID)
+        end
+      end
     end
   end
 

spec/fixtures/test_api_requests.rb

@@ -47,6 +47,11 @@ def api_client_error(type = :json)
       .to_return defaults.merge(body:body, status:404)
   end
 
+  def api_client_error
+    @rspec.stub_request(:get, 'example.com/api/my_temp_resources/1')
+      .to_return response(body:{ 'error' => '422 Unprocessable Entity' }, status:422)
+  end
+
   def api_description
     @rspec.stub_request(:any, 'example.com/api')
       .to_return response(body:schema, headers:{ 'Cache-Control' => 'max-age=3600, public' })
@@ -57,6 +62,11 @@ def unknown_instance
       .to_return response(body:{ 'error' => '404 Not Found' }, status:404)
   end
 
+  def invalid_unknown_instance
+    @rspec.stub_request(:get, 'example.com/api/my_temp_resources/1')
+      .to_return response(body:'Unparseable Not Found', status:404)
+  end
+
   def known_instance
     @rspec.stub_request(:get, 'example.com/api/my_temp_resources/1')
       .to_return response(body:{ 'name' => 'Resource Name' })