FFM-8670: Feature flag rule not being evaluated for a given attribute

* Fix evaluation issue where a boolean is returned instead of a value
* Include test case

lib/ff/ruby/server/sdk/api/evaluator.rb

@@ -142,7 +142,7 @@ def get_attr_value(target, attribute)
         return target.send(attribute)
       else
 
-        result = target.attributes.key?(attribute)
+        result = target.attributes[attribute.to_sym]
 
         if result == nil
 

test/ff/ruby/server/sdk/evaluator_test.rb

@@ -0,0 +1,21 @@
+# File:  evaluator.rb
+# frozen_string_literal: true
+
+$LOAD_PATH.unshift File.expand_path("../lib", __dir__)
+
+require "securerandom"
+require "minitest/autorun"
+require "test_helper"
+
+require "ff/ruby/server/sdk"
+require "test/unit"
+
+class TestEvaluator < ActiveSupport::TestCase
+
+    test '#get_attr_value' do
+        mock = Minitest::Mock.new
+        mock.expect :apply, true
+
+        assert_mock mock
+    end 
+end