diff --git a/t/CMDTEST_file_equal.rb b/t/CMDTEST_file_equal.rb
index 9ddaf42..6b1b40c 100644
--- a/t/CMDTEST_file_equal.rb
+++ b/t/CMDTEST_file_equal.rb
@@ -10,7 +10,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
 
   def test_file_equal_CORRECT_EMPTY
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {}",
+      "file_open('foo', 'w') {}",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', ''",
@@ -31,7 +31,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
   def test_file_equal_INCORRECT_EMPTY
 
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {|f| f.puts 'hello world' }",
+      "file_open('foo', 'w') {|f| f.puts 'hello world' }",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', ''",
@@ -56,7 +56,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
   def test_file_equal_CORRECT_NO_LINES
 
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {}",
+      "file_open('foo', 'w') {}",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', []",
@@ -78,7 +78,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
   def test_file_equal_INCORRECT_NO_LINES
 
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {|f| f.puts 'hello world' }",
+      "file_open('foo', 'w') {|f| f.puts 'hello world' }",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', []",
@@ -102,7 +102,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
   def test_file_equal_CORRECT_LINE
 
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {|f| f.puts 'hello world' }",
+      "file_open('foo', 'w') {|f| f.puts 'hello world' }",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', [ 'hello world' ]",
@@ -122,7 +122,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
   def test_file_equal_INCORRECT_LINE
 
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {}",
+      "file_open('foo', 'w') {}",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', [ 'hello world' ]",
@@ -146,7 +146,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
   def test_file_equal_CORRECT_2_LINES
 
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {|f| f.puts 'hello'; f.puts 'world' }",
+      "file_open('foo', 'w') {|f| f.puts 'hello'; f.puts 'world' }",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', [ 'hello', 'world' ]",
@@ -166,7 +166,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
   def test_file_equal_INCORRECT_2_LINES
 
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {}",
+      "file_open('foo', 'w') {}",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', [ 'hello', 'world' ]",
@@ -211,7 +211,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
   def test_file_equal_FILE_IS_DIRECTORY
 
     create_CMDTEST_foo [
-      "Dir.mkdir 'foo'",
+      "dir_mkdir 'foo'",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', ''",
@@ -235,7 +235,7 @@ class CMDTEST_file_equal < Cmdtest::Testcase
     return unless ! windows?
 
     create_CMDTEST_foo [
-      "File.symlink 'foo', 'foo'",
+      "file_symlink 'foo', 'foo'",
       "",
       "cmd 'true.rb' do",
       "    file_equal 'foo', ''",
diff --git a/t/CMDTEST_file_not_equal.rb b/t/CMDTEST_file_not_equal.rb
index f9a9c3f..1d02914 100644
--- a/t/CMDTEST_file_not_equal.rb
+++ b/t/CMDTEST_file_not_equal.rb
@@ -10,7 +10,7 @@ class CMDTEST_file_not_equal < Cmdtest::Testcase
 
   def test_file_not_equal_CORRECT
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {|f| f.puts 'hello' }",
+      "file_open('foo', 'w') {|f| f.puts 'hello' }",
       "",
       "cmd 'true.rb' do",
       "    file_not_equal 'foo', ['world']",
@@ -30,7 +30,7 @@ class CMDTEST_file_not_equal < Cmdtest::Testcase
 
   def test_file_not_equal_INCORRECT
     create_CMDTEST_foo [
-      "File.open('foo', 'w') {|f| f.puts 'hello' }",
+      "file_open('foo', 'w') {|f| f.puts 'hello' }",
       "",
       "cmd 'true.rb' do",
       "    file_not_equal 'foo', ['hello']",
diff --git a/t/CMDTEST_ignore_file.rb b/t/CMDTEST_ignore_file.rb
index bc0c27b..a038dad 100644
--- a/t/CMDTEST_ignore_file.rb
+++ b/t/CMDTEST_ignore_file.rb
@@ -74,7 +74,7 @@ class CMDTEST_ignore_file < Cmdtest::Testcase
   def test_ignore_file_IGNORED_IN_SUBDIR
     create_CMDTEST_foo [
       "ignore_file 'dir/bbb'",
-      "Dir.mkdir 'dir'",
+      "dir_mkdir 'dir'",
       "",
       "cmd 'touch.rb aaa bbb dir/aaa dir/bbb' do",
       "  created_files 'aaa', 'bbb', 'dir/aaa'",
@@ -95,7 +95,7 @@ class CMDTEST_ignore_file < Cmdtest::Testcase
   def test_ignore_file_PATH_MATTERS
     create_CMDTEST_foo [
       "ignore_file 'bbb'",
-      "Dir.mkdir 'dir'",
+      "dir_mkdir 'dir'",
       "",
       "cmd 'touch.rb aaa bbb dir/aaa dir/bbb' do",
       "  created_files 'aaa', 'dir/aaa', 'dir/bbb'",
diff --git a/t/CMDTEST_import_file.rb b/t/CMDTEST_import_file.rb
index 41158c6..bdee802 100644
--- a/t/CMDTEST_import_file.rb
+++ b/t/CMDTEST_import_file.rb
@@ -39,8 +39,8 @@ class CMDTEST_import_file < Cmdtest::Testcase
     create_file "file2.txt", "This is file2.txt\n"
 
     create_CMDTEST_foo [
-      "Dir.mkdir('dir')",
-      "Dir.chdir('dir')",
+      "dir_mkdir('dir')",
+      "chdir('dir')",
       "import_file 'file1.txt', 'qwerty1.txt'",
       "import_file 'file2.txt', 'subdir/qwerty2.txt'",
       "",
diff --git a/t/CMDTEST_misc.rb b/t/CMDTEST_misc.rb
index 2759044..363e3e9 100644
--- a/t/CMDTEST_misc.rb
+++ b/t/CMDTEST_misc.rb
@@ -120,8 +120,8 @@ class CMDTEST_misc < Cmdtest::Testcase
 
   def test_existing_files_is_OK
     create_CMDTEST_foo [
-      "File.open('before1', 'w') {}",
-      "File.open('before2', 'w') {}",
+      "file_open('before1', 'w') {}",
+      "file_open('before2', 'w') {}",
       "cmd 'true.rb' do",
       "end",
     ]
@@ -156,8 +156,8 @@ class CMDTEST_misc < Cmdtest::Testcase
 
   def test_several_actual_created_files_will_give_error
     create_CMDTEST_foo [
-      "File.open('before1', 'w') {}",
-      "File.open('before2', 'w') {}",
+      "file_open('before1', 'w') {}",
+      "file_open('before2', 'w') {}",
       "cmd 'echo.rb x > a && echo.rb x > b' do",
       "end",
     ]
@@ -177,7 +177,7 @@ class CMDTEST_misc < Cmdtest::Testcase
 
   def test_actual_removed_file_will_give_error
     create_CMDTEST_foo [
-      "File.open('before', 'w') {}",
+      "file_open('before', 'w') {}",
       "cmd 'rm.rb before' do",
       "end",
     ]
@@ -197,9 +197,9 @@ class CMDTEST_misc < Cmdtest::Testcase
 
   def test_several_actual_removed_files_will_give_error
     create_CMDTEST_foo [
-      "File.open('before1', 'w') {}",
-      "File.open('before2', 'w') {}",
-      "File.open('before3', 'w') {}",
+      "file_open('before1', 'w') {}",
+      "file_open('before2', 'w') {}",
+      "file_open('before3', 'w') {}",
       "cmd 'rm.rb before1 before2' do",
       "end",
     ]
@@ -220,10 +220,10 @@ class CMDTEST_misc < Cmdtest::Testcase
   def test_actual_changed_files_will_give_error
     # NOTE: order of writing/testing is important below
     create_CMDTEST_foo <<'_END_'
-      File.open('changed1', 'w') {}
-      File.open('changed2', 'w') {}
+      file_open('changed1', 'w') {}
+      file_open('changed2', 'w') {}
 
-      File.open('script.rb', 'w') do |f|
+      file_open('script.rb', 'w') do |f|
           f.puts 't1 = File.mtime("changed2")'
           f.puts 'while File.mtime("changed2") == t1'
           f.puts '    File.open("changed2", "w") {|f| f.puts 111 }'
@@ -250,9 +250,9 @@ _END_
 
   def test_mix_of_actual_created_removed_files_will_give_error
     create_CMDTEST_foo [
-      "File.open('before1', 'w') {}",
-      "File.open('before2', 'w') {}",
-      "File.open('before3', 'w') {}",
+      "file_open('before1', 'w') {}",
+      "file_open('before2', 'w') {}",
+      "file_open('before3', 'w') {}",
       "cmd 'rm.rb before1 before2 && echo.rb x > a && echo.rb x > b' do",
       "end",
     ]
@@ -275,10 +275,10 @@ _END_
 
   def test_mix_of_all_errros
     create_CMDTEST_foo <<'_END_'
-      File.open('before1', 'w') {}
-      File.open('before2', 'w') {}
-      File.open('before3', 'w') {}
-      File.open('script.rb', 'w') do |f|
+      file_open('before1', 'w') {}
+      file_open('before2', 'w') {}
+      file_open('before3', 'w') {}
+      file_open('script.rb', 'w') do |f|
           f.puts 'File.unlink "before1"'
           f.puts 'File.unlink "before2"'
           f.puts 'File.open("a", "w") {}'
@@ -320,8 +320,8 @@ _END_
 
   def test_removed_files
     create_CMDTEST_foo [
-      "File.open('file1', 'w') {}",
-      "File.open('file2', 'w') {}",
+      "file_open('file1', 'w') {}",
+      "file_open('file2', 'w') {}",
       "",
       "cmd 'rm.rb file1' do",
       "    comment 'removed_files'",
@@ -340,8 +340,8 @@ _END_
 
   def test_FAILED_removed_files
     create_CMDTEST_foo [
-      "File.open('file1', 'w') {}",
-      "File.open('file2', 'w') {}",
+      "file_open('file1', 'w') {}",
+      "file_open('file2', 'w') {}",
       "",
       "cmd 'true.rb' do",
       "    comment 'FAILED removed_files'",
@@ -364,8 +364,8 @@ _END_
 
   def test_changed_files
     create_CMDTEST_foo [
-      "File.open('file1', 'w') {}",
-      "File.open('file2', 'w') {}",
+      "file_open('file1', 'w') {}",
+      "file_open('file2', 'w') {}",
       "",
       "cmd 'sleep.rb 1 && touch.rb file1' do",
       "    comment 'changed_files'",
@@ -385,8 +385,8 @@ _END_
   def test_FAILED_changed_files
 
     create_CMDTEST_foo [
-      "File.open('file1', 'w') {}",
-      "File.open('file2', 'w') {}",
+      "file_open('file1', 'w') {}",
+      "file_open('file2', 'w') {}",
       "",
       "cmd 'true.rb' do",
       "    comment 'FAILED changed_files'",
@@ -409,8 +409,8 @@ _END_
 
   def test_created_files
     create_CMDTEST_foo [
-      "File.open('file1', 'w') {}",
-      "File.open('file2', 'w') {}",
+      "file_open('file1', 'w') {}",
+      "file_open('file2', 'w') {}",
       "",
       "cmd 'touch.rb file3' do",
       "    comment 'created_files'",
@@ -429,8 +429,8 @@ _END_
 
   def test_FAILED_created_files
     create_CMDTEST_foo [
-      "File.open('file1', 'w') {}",
-      "File.open('file2', 'w') {}",
+      "file_open('file1', 'w') {}",
+      "file_open('file2', 'w') {}",
       "",
       "cmd 'true.rb' do",
       "    comment 'FAILED created_files'",
@@ -853,8 +853,8 @@ _END_
     create_CMDTEST_foo [
       "File.symlink 'non-existing', 'non-existing-link'",
       "",
-      "File.open('existing', 'w') {}",
-      "File.symlink 'existing', 'existing-link'",
+      "file_open('existing', 'w') {}",
+      "file_symlink 'existing', 'existing-link'",
       "",
       "cmd 'true.rb' do",
       "end",
@@ -871,9 +871,9 @@ _END_
 
   def test_file_with_mtime_in_future
     create_CMDTEST_foo [
-      "File.open('future-file', 'w') {}",
+      "file_open('future-file', 'w') {}",
       "future = Time.now + 86400",
-      "File.utime future, future, 'future-file'",
+      "file_utime future, future, 'future-file'",
       "",
       "cmd 'true.rb' do",
       "end",