Document and test all available gemrc configuration keys

Document missing gemrc configuration keys. The documented configuration key
order aligns with the following part.

https://github.com/ruby/rubygems/blob/287175d4ae57340e22c6f1d21da1489d7dac35c5/lib/rubygems/config_file.rb#L240-L257

Add and update tests for missing gemrc configuration use_psych and gemhome key
assertions.

Fix test_initialize_global_gem_cache_gemrc and
test_initialize_concurrent_downloads to test with symbolic keys,
as global_gem_cache and use_psych keys are documented as a symbolic key.

Author: junaruga

lib/rubygems/config_file.rb

@@ -26,9 +26,22 @@
 # RubyGems options use symbol keys.  Valid options are:
 #
 # +:backtrace+:: See #backtrace
-# +:sources+:: Sets Gem::sources
+# +:bulk_threshold+:: See #bulk_threshold
 # +:verbose+:: See #verbose
+# +:update_sources+:: See #update_sources
 # +:concurrent_downloads+:: See #concurrent_downloads
+# +:cert_expiration_length_days+:: See #cert_expiration_length_days
+# +:install_extension_in_lib+:: See #install_extension_in_lib
+# +:ipv4_fallback_enabled+:: See #ipv4_fallback_enabled
+# +:global_gem_cache+:: See #global_gem_cache
+# +:use_psych+:: See #use_psych
+# +:gemhome+:: See #home
+# +:gempath+:: See #path
+# +:sources+:: Sets Gem::sources
+# +:disable_default_gem_server+:: See #disable_default_gem_server
+# +:ssl_verify_mode+:: See #ssl_verify_mode
+# +:ssl_ca_cert+:: See #ssl_ca_cert
+# +:ssl_client_cert+:: See #ssl_client_cert
 #
 # gemrc files may exist in various locations and are read and merged in
 # the following order:

test/rubygems/test_gem_config_file.rb

@@ -53,6 +53,7 @@ def test_initialize
       fp.puts ":sources:"
       fp.puts "  - http://more-gems.example.com"
       fp.puts "install: --wrappers"
+      fp.puts ":gemhome: /tmp/gems"
       fp.puts ":gempath:"
       fp.puts "- /usr/ruby/1.8/lib/ruby/gems/1.8"
       fp.puts "- /var/ruby/1.8/gem_home"
@@ -61,6 +62,7 @@ def test_initialize
       fp.puts ":cert_expiration_length_days: 28"
       fp.puts ":install_extension_in_lib: false"
       fp.puts ":ipv4_fallback_enabled: true"
+      fp.puts ":use_psych: true"
     end
 
     util_config_file
@@ -70,13 +72,15 @@ def test_initialize
     assert_equal false, @cfg.update_sources
     assert_equal %w[http://more-gems.example.com], @cfg.sources
     assert_equal "--wrappers", @cfg[:install]
+    assert_equal "/tmp/gems", @cfg.home
     assert_equal(["/usr/ruby/1.8/lib/ruby/gems/1.8", "/var/ruby/1.8/gem_home"],
                  @cfg.path)
     assert_equal 0, @cfg.ssl_verify_mode
     assert_equal "/etc/ssl/certs", @cfg.ssl_ca_cert
     assert_equal 28, @cfg.cert_expiration_length_days
     assert_equal false, @cfg.install_extension_in_lib
     assert_equal true, @cfg.ipv4_fallback_enabled
+    assert_equal true, @cfg.use_psych
   end
 
   def test_initialize_ipv4_fallback_enabled_env
@@ -105,17 +109,27 @@ def test_initialize_global_gem_cache_env
 
   def test_initialize_global_gem_cache_gemrc
     File.open @temp_conf, "w" do |fp|
-      fp.puts "global_gem_cache: true"
+      fp.puts ":global_gem_cache: true"
     end
 
     util_config_file %W[--config-file #{@temp_conf}]
 
     assert_equal true, @cfg.global_gem_cache
   end
 
+  def test_initialize_use_psych_env
+    orig_use_psych = ENV["RUBYGEMS_USE_PSYCH"]
+    ENV["RUBYGEMS_USE_PSYCH"] = "true"
+    util_config_file %W[--config-file #{@temp_conf}]
+
+    assert_equal true, @cfg.use_psych
+  ensure
+    ENV["RUBYGEMS_USE_PSYCH"] = orig_use_psych
+  end
+
   def test_initialize_concurrent_downloads
     File.open @temp_conf, "w" do |fp|
-      fp.puts "concurrent_downloads: 2"
+      fp.puts ":concurrent_downloads: 2"
     end
 
     util_config_file %W[--config-file #{@temp_conf}]