diff --git a/Gemfile b/Gemfile
index 009240b..5b908a9 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,6 +5,7 @@ gemspec
 rails_version = ENV["RAILS_VERSION"] == "edge" ? { github: "rails/rails" } : ENV["RAILS_VERSION"]
 gem "actionpack", rails_version
 gem "activesupport", rails_version
+gem "concurrent-ruby", "1.3.4"
 
 graphql_version = ENV["GRAPHQL_VERSION"] == "edge" ? { github: "rmosolgo/graphql-ruby", ref: "interpreter-without-legacy" } : ENV["GRAPHQL_VERSION"]
 gem "graphql", graphql_version
diff --git a/lib/graphql/client/erb.rb b/lib/graphql/client/erb.rb
index d4b42fd..d549f29 100644
--- a/lib/graphql/client/erb.rb
+++ b/lib/graphql/client/erb.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 require "action_view"
+require "logger"
 
 module GraphQL
   class Client
diff --git a/lib/rubocop/cop/graphql/overfetch.rb b/lib/rubocop/cop/graphql/overfetch.rb
index 182fe83..f30f1bd 100644
--- a/lib/rubocop/cop/graphql/overfetch.rb
+++ b/lib/rubocop/cop/graphql/overfetch.rb
@@ -42,7 +42,7 @@ def investigate(processed_source)
 
           visitor.fields.each do |field, count|
             next if count > 0
-            add_offense(nil, message: "GraphQL field '#{field}' query but was not used in template.")
+            add_offense(visitor.ranges[field], message: "GraphQL field '#{field}' query but was not used in template.")
           end
         end
 
diff --git a/test/test_client_fetch.rb b/test/test_client_fetch.rb
index e438f70..dbf99a4 100644
--- a/test/test_client_fetch.rb
+++ b/test/test_client_fetch.rb
@@ -79,10 +79,10 @@ def self.resolve_type(_type, _obj, _ctx)
     refute response.data
 
     refute_empty response.errors
-    assert_equal "Field 'err' doesn't exist on type 'Query'", response.errors[:data][0]
+    assert_includes response.errors[:data][0], "Field 'err' doesn't exist on type 'Query'"
 
     refute_empty response.errors.all
-    assert_equal "Field 'err' doesn't exist on type 'Query'", response.errors[:data][0]
+    assert_includes response.errors[:data][0], "Field 'err' doesn't exist on type 'Query'"
   end
 
   def test_failed_response
diff --git a/test/test_rubocop_heredoc.rb b/test/test_rubocop_heredoc.rb
index e1a5586..57fd011 100644
--- a/test/test_rubocop_heredoc.rb
+++ b/test/test_rubocop_heredoc.rb
@@ -9,85 +9,85 @@ def setup
   end
 
   def test_good_graphql_heredoc
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       Query = Client.parse <<'GRAPHQL'
         { version }
 GRAPHQL
     RUBY
 
-    assert_empty @cop.offenses.map(&:message)
+    assert_empty result.offenses.map(&:message)
   end
 
   def test_good_graphql_dash_heredoc
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       Query = Client.parse <<-'GRAPHQL'
         { version }
       GRAPHQL
     RUBY
 
-    assert_empty @cop.offenses.map(&:message)
+    assert_empty result.offenses.map(&:message)
   end
 
   def test_good_graphql_squiggly_heredoc
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       Query = Client.parse <<~'GRAPHQL'
         { version }
       GRAPHQL
     RUBY
 
-    assert_empty @cop.offenses.map(&:message)
+    assert_empty result.offenses.map(&:message)
   end
 
   def test_bad_graphql_heredoc
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       Query = Client.parse <<GRAPHQL
         { version }
 GRAPHQL
     RUBY
 
-    assert_equal 1, @cop.offenses.count
-    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", @cop.offenses.first.message
+    assert_equal 1, result.offenses.count
+    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", result.offenses.first.message
   end
 
   def test_bad_graphql_dash_heredoc
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       Query = Client.parse <<-GRAPHQL
         { version }
       GRAPHQL
     RUBY
 
-    assert_equal 1, @cop.offenses.count
-    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", @cop.offenses.first.message
+    assert_equal 1, result.offenses.count
+    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", result.offenses.first.message
   end
 
   def test_bad_graphql_squiggly_heredoc
     skip if RUBY_VERSION < "2.3"
 
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       Query = Client.parse <<~GRAPHQL
         { version }
       GRAPHQL
     RUBY
 
-    assert_equal 1, @cop.offenses.count
-    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", @cop.offenses.first.message
+    assert_equal 1, result.offenses.count
+    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", result.offenses.first.message
   end
 
   def test_bad_graphql_heredoc_with_interpolation
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       field = "version"
       Query = Client.parse <<-GRAPHQL
         { \#{field} }
       GRAPHQL
     RUBY
 
-    assert_equal 2, @cop.offenses.count
-    assert_equal "GraphQL/Heredoc: Do not interpolate variables into GraphQL queries, used variables instead.", @cop.offenses[0].message
-    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", @cop.offenses[1].message
+    assert_equal 2, result.offenses.count
+    assert_equal "GraphQL/Heredoc: Do not interpolate variables into GraphQL queries, used variables instead.", result.offenses[0].message
+    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", result.offenses[1].message
   end
 
   def test_bad_graphql_multiline_heredoc
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       Query = Client.parse <<GRAPHQL
         {
           version
@@ -95,12 +95,12 @@ def test_bad_graphql_multiline_heredoc
 GRAPHQL
     RUBY
 
-    assert_equal 1, @cop.offenses.count
-    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", @cop.offenses[0].message
+    assert_equal 1, result.offenses.count
+    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", result.offenses[0].message
   end
 
   def test_bad_graphql_multiline_dash_heredoc
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       Query = Client.parse <<-GRAPHQL
         {
           version
@@ -108,14 +108,14 @@ def test_bad_graphql_multiline_dash_heredoc
       GRAPHQL
     RUBY
 
-    assert_equal 1, @cop.offenses.count
-    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", @cop.offenses[0].message
+    assert_equal 1, result.offenses.count
+    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", result.offenses[0].message
   end
 
   def test_bad_graphql_multiline_squiggly_heredoc
     skip if RUBY_VERSION < "2.3"
 
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       Query = Client.parse <<~GRAPHQL
         {
           version
@@ -123,12 +123,12 @@ def test_bad_graphql_multiline_squiggly_heredoc
       GRAPHQL
     RUBY
 
-    assert_equal 1, @cop.offenses.count
-    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", @cop.offenses[0].message
+    assert_equal 1, result.offenses.count
+    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", result.offenses[0].message
   end
 
   def test_bad_graphql_multiline_heredoc_with_interpolation
-    investigate(@cop, <<-RUBY)
+    result = investigate(@cop, <<-RUBY)
       field = "version"
       Query = Client.parse <<-GRAPHQL
         {
@@ -137,9 +137,9 @@ def test_bad_graphql_multiline_heredoc_with_interpolation
       GRAPHQL
     RUBY
 
-    assert_equal 2, @cop.offenses.count
-    assert_equal "GraphQL/Heredoc: Do not interpolate variables into GraphQL queries, used variables instead.", @cop.offenses[0].message
-    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", @cop.offenses[1].message
+    assert_equal 2, result.offenses.count
+    assert_equal "GraphQL/Heredoc: Do not interpolate variables into GraphQL queries, used variables instead.", result.offenses[0].message
+    assert_equal "GraphQL/Heredoc: GraphQL heredocs should be quoted. <<-'GRAPHQL'", result.offenses[1].message
   end
 
   private
@@ -148,6 +148,5 @@ def investigate(cop, src)
     processed_source = RuboCop::ProcessedSource.new(src, RUBY_VERSION.to_f)
     commissioner = RuboCop::Cop::Commissioner.new([cop], [], raise_error: true)
     commissioner.investigate(processed_source)
-    commissioner
   end
 end
diff --git a/test/test_rubocop_overfetch.rb b/test/test_rubocop_overfetch.rb
index 5d8c233..5f6fee6 100644
--- a/test/test_rubocop_overfetch.rb
+++ b/test/test_rubocop_overfetch.rb
@@ -12,24 +12,24 @@ def setup
   end
 
   def test_all_fields_used
-    investigate(@cop, "#{Root}/views/users/show.html.erb")
+    result = investigate(@cop, "#{Root}/views/users/show.html.erb")
 
-    assert_empty @cop.offenses.map(&:message)
+    assert_empty result.offenses.map(&:message)
   end
 
   def test_all_fields_used_with_safe_navigation_operator
     skip if RUBY_VERSION < "2.3"
 
-    investigate(@cop, "#{Root}/views/users/show-2-3.html.erb")
+    result = investigate(@cop, "#{Root}/views/users/show-2-3.html.erb")
 
-    assert_empty @cop.offenses.map(&:message)
+    assert_empty result.offenses.map(&:message)
   end
 
   def test_field_unused
-    investigate(@cop, "#{Root}/views/users/overfetch.html.erb")
+    result = investigate(@cop, "#{Root}/views/users/overfetch.html.erb")
 
-    assert_equal 1, @cop.offenses.count
-    assert_equal "GraphQL/Overfetch: GraphQL field 'birthday' query but was not used in template.", @cop.offenses.first.message
+    assert_equal 1, result.offenses.count
+    assert_equal "GraphQL/Overfetch: GraphQL field 'birthday' query but was not used in template.", result.offenses.first.message
   end
 
   private
@@ -37,8 +37,7 @@ def test_field_unused
   def investigate(cop, path)
     engine = GraphQL::Client::ERB.new(File.read(path))
     processed_source = RuboCop::ProcessedSource.new(engine.src.dup, RUBY_VERSION.to_f, path)
-    commissioner = RuboCop::Cop::Commissioner.new([cop], [], raise_error: true)
+    commissioner = RuboCop::Cop::Commissioner.new([cop], [cop], raise_error: true)
     commissioner.investigate(processed_source)
-    commissioner
   end
 end