Add file_system specs

lib/langchain/tool/file_system/file_system.rb

@@ -29,6 +29,8 @@ def read_file(file_path:)
 
     def write_to_file(file_path:, content:)
       File.write(file_path, content)
+    rescue Errno::EACCES
+      "Permission denied: #{file_path}"
     end
   end
 end

spec/langchain/tool/file_system_spec.rb

@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+RSpec.describe Langchain::Tool::FileSystem do
+  subject { described_class.new }
+
+  context "directory operations" do
+    let(:directory_path) { "directory/path" }
+    let(:entries) { ["file1.txt", "file2.rb"] }
+
+    it "lists a directory" do
+      allow(Dir).to receive(:entries).with(directory_path).and_return(entries)
+      response = subject.list_directory(directory_path: directory_path)
+      expect(response).to eq(entries)
+    end
+
+    it "returns a no such directory error" do
+      allow(Dir).to receive(:entries).with(directory_path).and_raise(Errno::ENOENT)
+      response = subject.list_directory(directory_path: directory_path)
+      expect(response).to eq("No such directory: #{directory_path}")
+    end
+  end
+
+  context "file operations" do
+    context "writes to a file" do
+      let(:file_path) { "path/to/file.rb" }
+      let(:content) { "file contents" }
+
+      it "successfully writes" do
+        allow(File).to receive(:write).with(file_path, content)
+        response = subject.write_to_file(file_path: file_path, content: content)
+        expect(response).to eq(nil)
+      end
+
+      it "returns a permission denied error" do
+        allow(File).to receive(:write).with(file_path, content).and_raise(Errno::EACCES)
+        response = subject.write_to_file(file_path: file_path, content: content)
+        expect(response).to eq("Permission denied: #{file_path}")
+      end
+    end
+
+    context "reads a file" do
+      let(:file_path) { "path/to/file.rb" }
+      let(:content) { "file contents" }
+
+      it "successfully reads" do
+        allow(File).to receive(:read).with(file_path).and_return(content)
+        response = subject.read_file(file_path: file_path)
+        expect(response).to eq(content)
+      end
+
+      it "returns an error" do
+        allow(File).to receive(:read).with(file_path).and_raise(Errno::ENOENT)
+        response = subject.read_file(file_path: file_path)
+        expect(response).to eq("No such file: #{file_path}")
+      end
+    end
+  end
+end