Refactor setup tests to not always pass --prefix

Standard usage should be tested by default. I will add a test for
`--prefix` once I fix that option since it's not working correctly at
the moment.

test/rubygems/helper.rb

@@ -397,6 +397,14 @@ def setup
     @orig_bindir = RbConfig::CONFIG["bindir"]
     RbConfig::CONFIG["bindir"] = File.join @gemhome, "bin"
 
+    @orig_sitelibdir = RbConfig::CONFIG["sitelibdir"]
+    new_sitelibdir = @orig_sitelibdir.sub(RbConfig::CONFIG["prefix"], @gemhome)
+    $LOAD_PATH.insert(Gem.load_path_insert_index, new_sitelibdir)
+    RbConfig::CONFIG["sitelibdir"] = new_sitelibdir
+
+    @orig_mandir = RbConfig::CONFIG["mandir"]
+    RbConfig::CONFIG["mandir"] = File.join @gemhome, "share", "man"
+
     Gem::Specification.unresolved_deps.clear
     Gem.use_paths(@gemhome)
 
@@ -468,6 +476,8 @@ def teardown
 
     Gem.ruby = @orig_ruby if @orig_ruby
 
+    RbConfig::CONFIG['mandir'] = @orig_mandir
+    RbConfig::CONFIG['sitelibdir'] = @orig_sitelibdir
     RbConfig::CONFIG['bindir'] = @orig_bindir
 
     Gem.instance_variable_set :@default_specifications_dir, nil

test/rubygems/test_gem_commands_setup_command.rb

@@ -14,9 +14,7 @@ class TestGemCommandsSetupCommand < Gem::TestCase
   def setup
     super
 
-    @install_dir = File.join @tempdir, 'install'
     @cmd = Gem::Commands::SetupCommand.new
-    @cmd.options[:prefix] = @install_dir
 
     filelist = %w[
       bin/gem
@@ -269,7 +267,7 @@ def test_install_default_bundler_gem_with_destdir_flag
   end
 
   def test_remove_old_lib_files
-    lib                   = File.join @install_dir, 'lib'
+    lib                   = RbConfig::CONFIG["sitelibdir"]
     lib_rubygems          = File.join lib, 'rubygems'
     lib_bundler           = File.join lib, 'bundler'
     lib_rubygems_defaults = File.join lib_rubygems, 'defaults'
@@ -300,7 +298,7 @@ def test_remove_old_lib_files
   end
 
   def test_remove_old_man_files
-    man = File.join @install_dir, 'man'
+    man = File.join RbConfig::CONFIG['mandir'], 'man'
 
     ruby_1             = File.join man, 'man1', 'ruby.1'
     bundle_b_1         = File.join man, 'man1', 'bundle-b.1'
@@ -406,14 +404,14 @@ def gem_install_with_plugin(name)
   end
 
   def default_gem_bin_path
-    File.join @install_dir, 'bin', 'gem'
+    File.join RbConfig::CONFIG['bindir'], 'gem'
   end
 
   def default_bundle_bin_path
-    File.join @install_dir, 'bin', 'bundle'
+    File.join RbConfig::CONFIG['bindir'], 'bundle'
   end
 
   def default_bundler_bin_path
-    File.join @install_dir, 'bin', 'bundler'
+    File.join RbConfig::CONFIG['bindir'], 'bundler'
   end
 end unless Gem.java_platform?