Added test_gems.rb for setup dependencies

Merged: https://github.com/ruby/ruby/pull/3086

spec/bundler/support/rubygems_ext.rb

@@ -109,7 +109,10 @@ module Spec
     end
 
     def test_gemfile
-      Path.root.join("test_gems.rb")
+      gemfile = Path.root.join("test_gems.rb")
+      # for Ruby core repository
+      gemfile = Path.root.join("tool/bundler/test_gems.rb") unless File.exist?(gemfile)
+      gemfile
     end
 
     def test_lockfile

tool/bundler/test_gems.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+gem "rack", "2.0.8"
+gem "rack-test", "~> 1.1"
+gem "artifice", "~> 0.6.0"
+gem "compact_index", "~> 0.11.0"
+gem "sinatra", "~> 2.0"
+gem "rake", "13.0.1"
+gem "builder", "~> 3.2"
+# ruby-graphviz is used by the viz tests
+gem "ruby-graphviz", "1.2.4" # for >= Ruby 2.3

tool/bundler/test_gems.rb.lock

@@ -0,0 +1,40 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    artifice (0.6)
+      rack-test
+    builder (3.2.4)
+    compact_index (0.11.0)
+    mustermann (1.1.1)
+      ruby2_keywords (~> 0.0.1)
+    rack (2.0.8)
+    rack-protection (2.0.8.1)
+      rack
+    rack-test (1.1.0)
+      rack (>= 1.0, < 3)
+    rake (13.0.1)
+    ruby-graphviz (1.2.4)
+    ruby2_keywords (0.0.2)
+    sinatra (2.0.8.1)
+      mustermann (~> 1.0)
+      rack (~> 2.0)
+      rack-protection (= 2.0.8.1)
+      tilt (~> 2.0)
+    tilt (2.0.10)
+
+PLATFORMS
+  java
+  ruby
+
+DEPENDENCIES
+  artifice (~> 0.6.0)
+  builder (~> 3.2)
+  compact_index (~> 0.11.0)
+  rack (= 2.0.8)
+  rack-test (~> 1.1)
+  rake (= 13.0.1)
+  ruby-graphviz (= 1.2.4)
+  sinatra (~> 2.0)
+
+BUNDLED WITH
+   2.2.0.dev