Refresh specs using File.dirname(__FILE__)

This follows upstream change ruby/spec#1067

spec/core/dir/shared/chroot.rb

@@ -2,7 +2,7 @@
   before :all do
     DirSpecs.create_mock_dirs
 
-    @real_root = "../" * (File.dirname(__FILE__).count('/') - 1)
+    @real_root = "../" * (__dir__.count('/') - 1)
     @ref_dir = File.join("/", File.basename(Dir["/*"].first))
   end
 
@@ -18,7 +18,7 @@
   compilations_ci = ENV["GITHUB_WORKFLOW"] == "Compilations"
 
   it "can be used to change the process' root directory" do
-    -> { Dir.send(@method, File.dirname(__FILE__)) }.should_not raise_error
+    -> { Dir.send(@method, __dir__) }.should_not raise_error
     File.should.exist?("/#{File.basename(__FILE__)}")
   end unless compilations_ci
 

spec/core/dir/shared/exist.rb

@@ -1,6 +1,6 @@
 describe :dir_exist, shared: true do
   it "returns true if the given directory exists" do
-    Dir.send(@method, File.dirname(__FILE__)).should be_true
+    Dir.send(@method, __dir__).should be_true
   end
 
   it "returns true for '.'" do
@@ -20,15 +20,15 @@
   end
 
   it "understands relative paths" do
-    Dir.send(@method, File.dirname(__FILE__) + '/../').should be_true
+    Dir.send(@method, __dir__ + '/../').should be_true
   end
 
   it "returns false if the given directory doesn't exist" do
     Dir.send(@method, 'y26dg27n2nwjs8a/').should be_false
   end
 
   it "doesn't require the name to have a trailing slash" do
-    dir = File.dirname(__FILE__)
+    dir = __dir__
     dir.sub!(/\/$/,'')
     Dir.send(@method, dir).should be_true
   end
@@ -52,7 +52,7 @@
 
   it "calls #to_path on non String arguments" do
     p = mock('path')
-    p.should_receive(:to_path).and_return(File.dirname(__FILE__))
+    p.should_receive(:to_path).and_return(__dir__)
     Dir.send(@method, p)
   end
 end

spec/core/io/eof_spec.rb

@@ -84,7 +84,7 @@
   end
 
   it "returns true on one-byte stream after single-byte read" do
-    File.open(File.dirname(__FILE__) + '/fixtures/one_byte.txt') { |one_byte|
+    File.open(__dir__ + '/fixtures/one_byte.txt') { |one_byte|
       one_byte.read(1)
       one_byte.should.eof?
     }