1 files changed, 62 insertions, 0 deletions
diff --git a/spec/support/matchers/be_n_plus_1_query.rb b/spec/support/matchers/be_n_plus_1_query.rb
new file mode 100644
index 00000000000..bbfd1897f04
--- /dev/null
+++ b/spec/support/matchers/be_n_plus_1_query.rb
@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+module Nplus1QueryHelpers
+  DEFAULT_THRESHOLD = 3
+
+  def with_threshold(threshold)
+    @threshold = threshold
+    self
+  end
+
+  def for_query(query)
+    @query = query
+    self
+  end
+
+  def threshold
+    @threshold || DEFAULT_THRESHOLD
+  end
+
+  def occurrences
+    @occurrences ||=
+      if @query
+        recorder.occurrences.select { |recorded, count| recorded =~ @query }
+      else
+        recorder.occurrences
+      end
+  end
+
+  def over_threshold
+    occurrences.select do |recorded, count|
+      count > threshold
+    end
+  end
+
+  def recorder
+    @recorder ||= ActiveRecord::QueryRecorder.new(&@subject_block)
+  end
+
+  def verify_count(&block)
+    @subject_block = block
+    over_threshold.present?
+  end
+
+  def failure_message
+    log_message = over_threshold.to_yaml
+    "The following queries are executed more than #{threshold} time(s):\n#{log_message}"
+  end
+end
+
+RSpec::Matchers.define :be_n_plus_1_query do
+  supports_block_expectations
+
+  include Nplus1QueryHelpers
+
+  match do |block|
+    verify_count(&block)
+  end
+
+  failure_message_when_negated do |actual|
+    failure_message
+  end
+end