migrate existing tests to `should` syntax

test/test_plugin_manager.rb

@@ -8,23 +8,28 @@ class TestPluginManager < JekyllUnitTest
     FileUtils.mv "Gemfile.old", "Gemfile"
   end
 
-  def test_requiring_from_bundler
+  context "JEKYLL_NO_BUNDLER_REQUIRE set to `nil`" do
+    should "require from bundler" do
       with_env("JEKYLL_NO_BUNDLER_REQUIRE", nil) do
         assert Jekyll::PluginManager.require_from_bundler,
                "require_from_bundler should return true."
         assert ENV["JEKYLL_NO_BUNDLER_REQUIRE"], "Gemfile plugins were not required."
       end
     end
+  end
 
-  def test_blocking_requiring_from_bundler
+  context "JEKYLL_NO_BUNDLER_REQUIRE set to `true`" do
+    should "not require from bundler" do
       with_env("JEKYLL_NO_BUNDLER_REQUIRE", "true") do
         assert_equal false, Jekyll::PluginManager.require_from_bundler,
                      "Gemfile plugins were required but shouldn't have been"
         assert ENV["JEKYLL_NO_BUNDLER_REQUIRE"]
       end
     end
+  end
 
-  def test_no_gemfile
+  context "JEKYLL_NO_BUNDLER_REQUIRE set to `nil` and no Gemfile present" do
+    should "not require from bundler" do
       with_env("JEKYLL_NO_BUNDLER_REQUIRE", nil) do
         with_no_gemfile do
           assert_equal false, Jekyll::PluginManager.require_from_bundler,
@@ -34,3 +39,4 @@ class TestPluginManager < JekyllUnitTest
       end
     end
   end
+end