Move default_editor_for_platform to Pry::Editor

The name strongly suggests that this method belongs to `Pry::Editor` and it
makes no sense to have it on `Pry` class.

lib/pry.rb

@@ -18,6 +18,7 @@ require 'pry/class_command'
 require 'pry/block_command'
 require 'pry/command_set'
 require 'pry/syntax_highlighter'
+require 'pry/editor'
 
 Pry::Commands = Pry::CommandSet.new unless defined?(Pry::Commands)
 
@@ -49,7 +50,6 @@ require 'pry/inspector'
 require 'pry/color_printer'
 require 'pry/pager'
 require 'pry/terminal'
-require 'pry/editor'
 require 'pry/indent'
 require 'pry/object_path'
 require 'pry/output'

lib/pry/config.rb

@@ -78,7 +78,7 @@ class Pry
 
         color: Pry::Helpers::BaseHelpers.use_ansi_codes?,
         default_window_size: 5,
-        editor: Pry.default_editor_for_platform,
+        editor: Pry::Editor.default,
         should_load_rc: true,
         should_load_local_rc: true,
         should_trap_interrupts: Pry::Helpers::Platform.jruby?,

lib/pry/editor.rb

@@ -2,6 +2,16 @@ require 'shellwords'
 
 class Pry
   class Editor
+    def self.default
+      return ENV['VISUAL'] if ENV['VISUAL'] && !ENV['VISUAL'].empty?
+      return ENV['EDITOR'] if ENV['EDITOR'] && !ENV['EDITOR'].empty?
+      return 'notepad' if Helpers::Platform.windows?
+
+      %w[editor nano vi].find do |editor|
+        Kernel.system("which #{editor} > /dev/null 2>&1")
+      end
+    end
+
     include Pry::Helpers::CommandHelpers
 
     attr_reader :pry_instance

lib/pry/pry_class.rb

@@ -306,16 +306,6 @@ you can add "Pry.config.windows_console_warning = false" to your pryrc.
     nil
   end
 
-  def self.default_editor_for_platform
-    return ENV['VISUAL'] if ENV['VISUAL'] && !ENV['VISUAL'].empty?
-    return ENV['EDITOR'] if ENV['EDITOR'] && !ENV['EDITOR'].empty?
-    return 'notepad' if Helpers::Platform.windows?
-
-    %w[editor nano vi].detect do |editor|
-      system("which #{editor} > /dev/null 2>&1")
-    end
-  end
-
   def self.auto_resize!
     Pry.config.input # by default, load Readline
 

spec/editor_spec.rb

@@ -16,6 +16,48 @@ describe Pry::Editor do
     @editor = Pry::Editor.new(Pry.new)
   end
 
+  describe ".default" do
+    context "when $VISUAL is defined" do
+      before { ENV['VISUAL'] = 'emacs' }
+      after { ENV['VISUAL'] = nil }
+
+      it "returns the value of $VISUAL" do
+        expect(described_class.default).to eq('emacs')
+      end
+    end
+
+    context "when $EDITOR is defined" do
+      before { ENV['EDITOR'] = 'vim' }
+      after { ENV['EDITOR'] = nil }
+
+      it "returns the value of $EDITOR" do
+        expect(described_class.default).to eq('vim')
+      end
+    end
+
+    context "when platform is Windows" do
+      before do
+        allow(Pry::Helpers::Platform).to receive(:windows?).and_return(true)
+      end
+
+      it "returns 'notepad'" do
+        expect(described_class.default).to eq('notepad')
+      end
+    end
+
+    context "when no editor is detected" do
+      before { allow(Kernel).to receive(:system) }
+
+      %w[editor nano vi].each do |text_editor_name|
+        it "shells out to find '#{text_editor_name}'" do
+          expect(Kernel).to receive(:system)
+            .with("which #{text_editor_name} > /dev/null 2>&1")
+          described_class.default
+        end
+      end
+    end
+  end
+
   describe "build_editor_invocation_string", skip: !Pry::Helpers::Platform.windows? do
     it 'should shell-escape files' do
       invocation_str = @editor.build_editor_invocation_string(@tf_path, 5, true)