1 files changed, 94 insertions, 0 deletions
diff --git a/activesupport/test/core_ext/file_test.rb b/activesupport/test/core_ext/file_test.rb
new file mode 100644
index 0000000000..186c863f91
--- /dev/null
+++ b/activesupport/test/core_ext/file_test.rb
@@ -0,0 +1,94 @@
+# frozen_string_literal: true
+
+require "abstract_unit"
+require "active_support/core_ext/file"
+
+class AtomicWriteTest < ActiveSupport::TestCase
+  def test_atomic_write_without_errors
+    contents = "Atomic Text"
+    File.atomic_write(file_name, Dir.pwd) do |file|
+      file.write(contents)
+      assert_not File.exist?(file_name)
+    end
+    assert File.exist?(file_name)
+    assert_equal contents, File.read(file_name)
+  ensure
+    File.unlink(file_name) rescue nil
+  end
+
+  def test_atomic_write_doesnt_write_when_block_raises
+    File.atomic_write(file_name) do |file|
+      file.write("testing")
+      raise "something bad"
+    end
+  rescue
+    assert_not File.exist?(file_name)
+  end
+
+  def test_atomic_write_preserves_file_permissions
+    contents = "Atomic Text"
+    File.open(file_name, "w", 0755) do |file|
+      file.write(contents)
+      assert File.exist?(file_name)
+    end
+    assert File.exist?(file_name)
+    assert_equal 0100755 & ~File.umask, file_mode
+    assert_equal contents, File.read(file_name)
+
+    File.atomic_write(file_name, Dir.pwd) do |file|
+      file.write(contents)
+      assert File.exist?(file_name)
+    end
+    assert File.exist?(file_name)
+    assert_equal 0100755 & ~File.umask, file_mode
+    assert_equal contents, File.read(file_name)
+  ensure
+    File.unlink(file_name) rescue nil
+  end
+
+  def test_atomic_write_preserves_default_file_permissions
+    contents = "Atomic Text"
+    File.atomic_write(file_name, Dir.pwd) do |file|
+      file.write(contents)
+      assert_not File.exist?(file_name)
+    end
+    assert File.exist?(file_name)
+    assert_equal File.probe_stat_in(Dir.pwd).mode, file_mode
+    assert_equal contents, File.read(file_name)
+  ensure
+    File.unlink(file_name) rescue nil
+  end
+
+  def test_atomic_write_preserves_file_permissions_same_directory
+    Dir.mktmpdir do |temp_dir|
+      File.chmod 0700, temp_dir
+
+      probed_permissions = File.probe_stat_in(temp_dir).mode.to_s(8)
+
+      File.atomic_write(File.join(temp_dir, file_name), &:close)
+
+      actual_permissions = File.stat(File.join(temp_dir, file_name)).mode.to_s(8)
+
+      assert_equal actual_permissions, probed_permissions
+    end
+  end
+
+  def test_atomic_write_returns_result_from_yielded_block
+    block_return_value = File.atomic_write(file_name, Dir.pwd) do |file|
+      "Hello world!"
+    end
+
+    assert_equal "Hello world!", block_return_value
+  ensure
+    File.unlink(file_name) rescue nil
+  end
+
+  private
+    def file_name
+      "atomic.file"
+    end
+
+    def file_mode
+      File.stat(file_name).mode
+    end
+end