ruby: add tests

ruby/ql/test/query-tests/performance/DatabaseQueryInLoop/DatabaseQueryInLoop.expected

@@ -0,0 +1,3 @@
+| DatabaseQueryInLoop.rb:11:13:11:52 | call to first | This call to a database query operation happens inside $@, and could be hoisted to a single call outside the loop. | DatabaseQueryInLoop.rb:10:9:12:11 | call to map | this loop |
+| DatabaseQueryInLoop.rb:16:20:16:59 | call to first | This call to a database query operation happens inside $@, and could be hoisted to a single call outside the loop. | DatabaseQueryInLoop.rb:15:9:21:11 | call to map | this loop |
+| DatabaseQueryInLoop.rb:19:17:19:56 | call to first | This call to a database query operation happens inside $@, and could be hoisted to a single call outside the loop. | DatabaseQueryInLoop.rb:18:13:20:15 | call to map | this loop |

ruby/ql/test/query-tests/performance/DatabaseQueryInLoop/DatabaseQueryInLoop.qlref

@@ -0,0 +1 @@
+queries/performance/DatabaseQueryInLoop.ql

ruby/ql/test/query-tests/performance/DatabaseQueryInLoop/DatabaseQueryInLoop.rb

@@ -0,0 +1,53 @@
+
+class User < ActiveRecord::Base
+end
+
+class DatabaseQueryInLoopTest
+    def test
+        ### These are bad
+
+        # simple query in loop
+        names.map do |name|
+            User.where(login: name).pluck(:id).first
+        end
+        
+        # nested loop
+        names.map do |name|
+            user = User.where(login: name).pluck(:id).first
+
+            ids.map do |user_id|
+                User.where(id: user_id).pluck(:id).first
+            end
+        end
+
+        ### These are OK
+
+        # Not in loop
+        User.where(login: owner_slug).pluck(:id).first
+
+        # Loops over constant array
+        %w(first-name second-name).map { |name| User.where(login: name).pluck(:id).first }
+
+        constant_names = [first-name, second-name]
+        constant_names.each do |name|
+            User.where(login: name).pluck(:id).first
+          end
+
+        # Loop traversal is influenced by query result
+        # raising an exception if the user is not found
+        names.map do |name|
+            user = User.where(login: name).pluck(:id).first
+            unless user
+                raise Error.new("User '#{name}' not found")
+            end
+        end
+
+        # skipping through the loop when users are not relevant
+        names.map do |name|
+            user = User.where(login: name).pluck(:id).first
+            if not isRelevant(user)
+                next
+            end
+        end
+    end
+end