Fix leaky tests:

- While working on ruby#9210, I found those leaky tests which break
  the test suite.
  They remove Bundler constants without setting them back.

  The reason it's not a problem on master is because there are no
  tests that install gems in the same process (all tests shell out
  to `bundle install`).

Author: Edouard-chin

bundler/spec/bundler/plugin/events_spec.rb

@@ -2,7 +2,17 @@
 
 RSpec.describe Bundler::Plugin::Events do
   context "plugin events" do
-    before { Bundler::Plugin::Events.send :reset }
+    before do
+      @old_constants = Bundler::Plugin::Events.constants.map {|name| [name, Bundler::Plugin::Events.const_get(name)] }
+      Bundler::Plugin::Events.send :reset
+    end
+
+    after do
+      Bundler::Plugin::Events.send(:reset)
+      Hash[@old_constants].each do |name, value|
+        Bundler::Plugin::Events.send(:define, name, value)
+      end
+    end
 
     describe "#define" do
       it "raises when redefining a constant" do

bundler/spec/bundler/plugin_spec.rb

@@ -279,6 +279,7 @@
         s.write "plugins.rb", code
       end
 
+      @old_constants = Bundler::Plugin::Events.constants.map {|name| [name, Bundler::Plugin::Events.const_get(name)] }
       Bundler::Plugin::Events.send(:reset)
       Bundler::Plugin::Events.send(:define, :EVENT1, "event-1")
       Bundler::Plugin::Events.send(:define, :EVENT2, "event-2")
@@ -291,6 +292,13 @@
       allow(index).to receive(:load_paths).with("foo-plugin").and_return([])
     end
 
+    after do
+      Bundler::Plugin::Events.send(:reset)
+      Hash[@old_constants].each do |name, value|
+        Bundler::Plugin::Events.send(:define, name, value)
+      end
+    end
+
     let(:code) { <<-RUBY }
       Bundler::Plugin::API.hook("event-1") { puts "hook for event 1" }
     RUBY