1 files changed, 13 insertions, 0 deletions
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 64f1c9f6cc..379c0c0758 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -1488,4 +1488,17 @@ class RelationTest < ActiveRecord::TestCase
       Array.send(:remove_method, :__omg__)
     end
   end
+
+  test "merge collapses wheres from the LHS only" do
+    left  = Post.where(title: "omg").where(comments_count: 1)
+    right = Post.where(title: "wtf").where(title: "bbq")
+
+    expected = [left.where_values[1]] + right.where_values
+    merged   = left.merge(right)
+
+    assert_equal expected, merged.where_values
+    assert !merged.to_sql.include?("omg")
+    assert merged.to_sql.include?("wtf")
+    assert merged.to_sql.include?("bbq")
+  end
 end